util: move virFile* functions from virutil.c to virfile.c

These all existed before virfile.c was created, and for some reason
weren't moved.

This is mostly straightfoward, although the syntax rule prohibiting
write() had to be changed to have an exception for virfile.c instead
of virutil.c.

This movement pointed out that there is a function called
virBuildPath(), and another almost identical function called
virFileBuildPath(). They really should be a single function, which
I'll take care of as soon as I figure out what the arglist should look
like.

tests/eventtest.c

@@ -1,7 +1,7 @@
 /*
  * eventtest.c: Test the libvirtd event loop impl
  *
- * Copyright (C) 2009, 2011 Red Hat, Inc.
+ * Copyright (C) 2009, 2011-2013 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -28,6 +28,7 @@
 
 #include "testutils.h"
 #include "internal.h"
+#include "virfile.h"
 #include "virthread.h"
 #include "virlog.h"
 #include "virutil.h"