API: make declaration of _LAST enum values conditional

Although this is a public API break, it only affects users that
were compiling against *_LAST values, and can be trivially
worked around without impacting compilation against older
headers, by the user defining VIR_ENUM_SENTINELS before using
libvirt.h.  It is not an ABI break, since enum values do not
appear as .so entry points.  Meanwhile, it prevents users from
using non-stable enum values without explicitly acknowledging
the risk of doing so.

See this list discussion:
https://www.redhat.com/archives/libvir-list/2012-January/msg00804.html

* include/libvirt/libvirt.h.in: Hide all sentinels behind
LIBVIRT_ENUM_SENTINELS, and add missing sentinels.
* src/internal.h (VIR_DEPRECATED): Allow inclusion after
libvirt.h.
(LIBVIRT_ENUM_SENTINELS): Expose sentinels internally.
* daemon/libvirtd.h: Use the sentinels.
* src/remote/remote_protocol.x (includes): Don't expose sentinels.
* python/generator.py (enum): Likewise.
* tests/cputest.c (cpuTestCompResStr): Silence compiler warning.
* tools/virsh.c (vshDomainStateReasonToString)
(vshDomainControlStateToString): Likewise.

daemon/libvirtd.h

@@ -1,7 +1,7 @@
 /*
  * libvirtd.h: daemon data structure definitions
  *
- * Copyright (C) 2006-2011 Red Hat, Inc.
+ * Copyright (C) 2006-2012 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -22,8 +22,10 @@
  */
 
 
-#ifndef QEMUD_INTERNAL_H__
-# define QEMUD_INTERNAL_H__
+#ifndef LIBVIRTD_H__
+# define LIBVIRTD_H__
+
+# define VIR_ENUM_SENTINELS
 
 # include <config.h>