Enforce the rule that .h files don't need to (redundantly)
include <config.h>.

* cfg.mk (sc_prohibit_config_h_in_headers): New rule.
(_virsh_includes): Delete; instead, inline a smaller number of
exclusions...
(exclude_file_name_regexp--sc_require_config_h)
(exclude_file_name_regexp--sc_require_config_h_first): ...here.
* daemon/libvirtd.h (includes): Fix offenders.
* src/driver.h (includes): Likewise.
* src/gnutls_1_0_compat.h (includes): Likewise.
* src/libxl/libxl_conf.h (includes): Likewise.
* src/libxl/libxl_driver.h (includes): Likewise.
* src/lxc/lxc_conf.h (includes): Likewise.
* src/lxc/lxc_driver.h (includes): Likewise.
* src/lxc/lxc_fuse.h (includes): Likewise.
* src/network/bridge_driver.h (includes): Likewise.
* src/phyp/phyp_driver.h (includes): Likewise.
* src/qemu/qemu_conf.h (includes): Likewise.
* src/util/virnetlink.h (includes): Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>