Implement SELinux/MAC checks for property service.

This is a set of changes to the init property service
implementation to apply a SELinux check over who can
change what properties. Also included control hooks
for the 'ctl' keys.

Change-Id: I5a18809bf5536f6459a36b6bf0d622b9f5061aa0
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>
diff --git a/init/init.h b/init/init.h
index e2d990e..b7e06c9 100644
--- a/init/init.h
+++ b/init/init.h
@@ -138,6 +138,7 @@
 
 #ifdef HAVE_SELINUX
 extern struct selabel_handle *sehandle;
+extern struct selabel_handle *sehandle_prop;
 extern int selinux_reload_policy(void);
 #endif