Fix the build if HAVE_AVAHI is not defined.

When an incoming RPC message is ready for processing,

  virNetServerClientDispatchRead()

will invoke the 'dispatchFunc' callback. This is set to

  virNetServerDispatchNewMessage

This function puts the message + client in a queue for processing by the thread
pool. The thread pool worker function is

  virNetServerHandleJob

The first thing this does is acquire an extra reference on the 'client'.

Unfortunately, between the time the message+client are put on the thread pool
queue, and the time the worker runs, the client object may have had its last
reference removed.

We clearly need to add the reference to the client object before putting the
client on the processing queue

* src/rpc/virnetserverclient.c: Add a reference to the client when
  invoking the dispatch function
* src/rpc/virnetserver.c: Don't acquire a reference to the client
  when in the worker thread

* src/rpc/virnetserver.c: Free mDNS object

If the virStateInitialize call fails we must shutdown libvirtd
since drivers will not be available. Just free'ing the virNetServer
is not sufficient, we must send a SIGTERM to ourselves so that
we interrupt the event loop and trigger a orderly shutdown

* daemon/libvirtd.c: Kill ourselves if state init fails
* src/rpc/virnetserver.c: Add some debugging to event loop

In preparation for a future patch adding new virFile APIs.

* src/util/files.h, src/util/files.c: Move...
* src/util/virfile.h, src/util/virfile.c: ...here, and rename
functions to virFile prefix.  Macro names are intentionally
left alone.
* *.c: All '#include "files.h"' uses changed.
* src/Makefile.am (UTIL_SOURCES): Reflect rename.
* cfg.mk (exclude_file_name_regexp--sc_prohibit_close): Likewise.
* src/libvirt_private.syms: Likewise.
* docs/hacking.html.in: Likewise.
* HACKING: Regenerate.

When replacing the default SEGV/ABORT/BUS signal handlers you
can't rely on the process being terminated after your custom
handler runs. It is neccessary to manually restore the default
handler and then re-raise the signal

* src/rpc/virnetserver.c: Restore default handler and raise
  signal

connectDBus is only used if HAVE_DBUS is set. Therefore mark
it as potentially unused.

V2: Remove policy kit references from virNetServer and use DBus APIs
    directly, if available.

Detected by Coverity.  No real harm in leaving these, but fixing
them cuts down on the noise for future analysis.

* src/rpc/virnetserver.c (virNetServerAddService): Delete unused
entry.
* src/util/sysinfo.c (virSysinfoRead): Delete dead assignment to
base.

* src/rpc/virnetserver.c: Free mdnsGroupName

Allow RPC servers to advertise themselves using MDNS,
via Avahi

* src/rpc/virnetserver.c, src/rpc/virnetserver.h: Allow
  registration of MDNS services via avahi
* src/rpc/virnetserverservice.c, src/rpc/virnetserverservice.h: Add
  API to fetch the listen port number
* src/rpc/virnetsocket.c, src/rpc/virnetsocket.h: Add API to
  fetch the local port number
* src/rpc/virnetservermdns.c, src/rpc/virnetservermdns.h: Represent
  an MDNS advertisement

To facilitate creation of new daemons providing XDR RPC services,
pull a lot of the libvirtd daemon code into a set of reusable
objects.

 * virNetServer: A server contains one or more services which
   accept incoming clients. It maintains the list of active
   clients. It has a list of RPC programs which can be used
   by clients. When clients produce a complete RPC message,
   the server passes this onto the corresponding program for
   handling, and queues any response back with the client.

 * virNetServerClient: Encapsulates a single client connection.
   All I/O for the client is handled, reading & writing RPC
   messages.

 * virNetServerProgram: Handles processing and dispatch of
   RPC method calls for a single RPC (program,version).
   Multiple programs can be registered with the server.

 * virNetServerService: Encapsulates socket(s) listening for
   new connections. Each service listens on a single host/port,
   but may have multiple sockets if on a dual IPv4/6 host.

Each new daemon now merely has to define the list of RPC procedures
& their handlers. It does not need to deal with any network related
functionality at all.