Inspired by Eric Blake

And from all related macros and functions.

Somehow the backend of this function was never implemented in
libvirt's netcf driver, and nobody noticed until now. (The required
netcf function was already in place, so nothing needs to change
there.)
* src/interface/netcf_driver.c: add in the backend function, and point
                                to it from the table of driver functions.

Prior to this patch, there was an inconsistent mix between GNU and C99.

For consistency, and potential portability to other compilers, stick
with the C99 vararg macro syntax.

* src/conf/cpu_conf.c (virCPUReportError): Use C99 rather than GNU
  vararg macro syntax.
* src/conf/domain_conf.c (virDomainReportError): Likewise.
* src/conf/domain_event.c (eventReportError): Likewise.
* src/conf/interface_conf.c (virInterfaceReportError): Likewise.
* src/conf/network_conf.c (virNetworkReportError): Likewise.
* src/conf/node_device_conf.h (virNodeDeviceReportError): Likewise.
* src/conf/secret_conf.h (virSecretReportError): Likewise.
* src/conf/storage_conf.h (virStorageReportError): Likewise.
* src/esx/esx_device_monitor.c (ESX_ERROR): Use C99 rather than
  GNU vararg macro syntax.
* src/esx/esx_driver.c (ESX_ERROR): Likewise.
* src/esx/esx_interface_driver.c (ESX_ERROR): Likewise.
* src/esx/esx_network_driver.c (ESX_ERROR): Likewise.
* src/esx/esx_secret_driver.c (ESX_ERROR): Likewise.
* src/esx/esx_storage_driver.c (ESX_ERROR): Likewise.
* src/esx/esx_util.c (ESX_ERROR): Likewise.
* src/esx/esx_vi.c (ESX_VI_ERROR): Likewise.
* src/esx/esx_vi_methods.c (ESX_VI_ERROR): Likewise.
* src/esx/esx_vi_types.c (ESX_VI_ERROR): Likewise.
* src/esx/esx_vmx.c (ESX_ERROR): Likewise.
* src/util/hostusb.c (usbReportError): Use C99 rather than GNU
  vararg macro syntax.
* src/util/json.c (virJSONError): Likewise.
* src/util/macvtap.c (ReportError): Likewise.
* src/util/pci.c (pciReportError): Likewise.
* src/util/stats_linux.c (virStatsError): Likewise.
* src/util/util.c (virUtilError): Likewise.
* src/util/xml.c (virXMLError): Likewise.
* src/xen/proxy_internal.c (virProxyError): Use C99 rather than
  GNU vararg macro syntax.
* src/xen/sexpr.c (virSexprError): Likewise.
* src/xen/xen_driver.c (xenUnifiedError): Likewise.
* src/xen/xen_hypervisor.c (virXenError): Likewise.
* src/xen/xen_inotify.c (virXenInotifyError): Likewise.
* src/xen/xend_internal.c (virXendError): Likewise.
* src/xen/xm_internal.c (xenXMError): Likewise.
* src/xen/xs_internal.c (virXenStoreError): Likewise.
* src/cpu/cpu.h (virCPUReportError): Use C99 rather than GNU
  vararg macro syntax.
* src/datatypes.c (virLibConnError): Likewise.
* src/interface/netcf_driver.c (interfaceReportError): Likewise.
* src/libvirt.c (virLibStreamError): Likewise.
* src/lxc/lxc_conf.h (lxcError): Likewise.
* src/network/bridge_driver.c (networkReportError): Likewise.
* src/nodeinfo.c (nodeReportError): Likewise.
* src/opennebula/one_conf.h (oneError): Likewise.
* src/openvz/openvz_conf.h (openvzError): Likewise.
* src/phyp/phyp_driver.c (PHYP_ERROR): Likewise.
* src/qemu/qemu_conf.h (qemuReportError): Likewise.
* src/remote/remote_driver.c (errorf): Likewise.
* src/security/security_driver.h (virSecurityReportError): Likewise.
* src/test/test_driver.c (testError): Likewise.
* src/uml/uml_conf.h (umlReportError): Likewise.
* src/vbox/vbox_driver.c (vboxError): Likewise.
* src/vbox/vbox_tmpl.c (vboxError): Likewise.

The open function returned -1 in case of an error, but -1 maps
to VIR_DRV_OPEN_DECLINED instead of VIR_DRV_OPEN_ERROR.

The virConnectPtr is no longer required for error reporting since
that is recorded in a thread local. Remove use of virConnectPtr
from all APIs in interface_conf.{h,c} and update all callers to
match

Introduce a number of new APIs to  expose some boolean properties
of objects, which cannot otherwise reliably determined, nor are
aspects of the XML configuration.

 * virDomainIsActive: Checking virDomainGetID is not reliable
   since it is not possible to distinguish between error condition
   and inactive domain for ID of -1.
 * virDomainIsPersistent: Check whether a persistent config exists
   for the domain

 * virNetworkIsActive: Check whether the network is active
 * virNetworkIsPersistent: Check whether a persistent config exists
   for the network

 * virStoragePoolIsActive: Check whether the storage pool is active
 * virStoragePoolIsPersistent: Check whether a persistent config exists
   for the storage pool

 * virInterfaceIsActive: Check whether the host interface is active

 * virConnectIsSecure: whether the communication channel to the
   hypervisor is secure
 * virConnectIsEncrypted: whether any network based commnunication
   channels are encrypted

NB, a channel can be secure, even if not encrypted, eg if it does
not involve the network, like a UNIX socket, or pipe.

 * include/libvirt/libvirt.h.in: Define public API
 * src/driver.h: Define internal driver API
 * src/libvirt.c: Implement public API entry point
 * src/libvirt_public.syms: Export API symbols
 * src/esx/esx_driver.c, src/lxc/lxc_driver.c,
   src/interface/netcf_driver.c, src/network/bridge_driver.c,
   src/opennebula/one_driver.c, src/openvz/openvz_driver.c,
   src/phyp/phyp_driver.c, src/qemu/qemu_driver.c,
   src/remote/remote_driver.c, src/test/test_driver.c,
   src/uml/uml_driver.c, src/vbox/vbox_tmpl.c,
   src/xen/xen_driver.c: Stub out driver tables

This patch adds the flag VIR_INTERFACE_XML_INACTIVE to
virInterfaceGetXMLDesc's flags. When it is*not* set (the default), the
live interface info will be returned in the XML (in particular, the IP
address(es) and netmask(s) will be retrieved by querying the interface
directly, rather than  reporting what's in the config file). The
backend of this is in netcf's ncf_if_xml_state() function.

* configure.in libvirt.spec.in: requires netcf >= 0.1.3
* include/libvirt/libvirt.h.in: adds flag VIR_INTERFACE_XML_INACTIVE
* src/conf/interface_conf.c src/interface/netcf_driver.c src/libvirt.c:
  update the parsing and backend routines accordingly
* tools/virsh.c: change interface edit to inactive definition and
  adds the inactive flag for interface dump

* daemon/qemud.c, src/Makefile.am: Adapt for changed paths
* src/interface_driver.c: Rename to src/interface/netcf_driver.c
* src/interface_driver.h: Rename to src/interface/netcf_driver.h

* src/libvirt.c: activate the interface drivers
* po/POTFILES.in: add the netcf driver as a source of localization strings
* src/interface_driver.c: NETCF_ENOMEM -> VIR_ERR_NO_MEMORY mapping was
  breaking syntax checking

* src/interface_driver.c src/interface_driver.h: the new driver
* src/Makefile.am qemud/Makefile.am qemud/qemud.c: hook the new driver
  in the build system and get ti activated by the daemon
* src/libvirt_private.syms: export needed symbols internally