Make sure it's a const

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3557 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/channel.h

@@ -100,7 +100,7 @@ struct ast_channel {
 	/*! Lock, can be used to lock a channel for some operations */
 	ast_mutex_t lock;			
 	/*! Procedure causing blocking */
-	char *blockproc;			
+	const char *blockproc;			
 
 	/*! Current application */
 	char *appl;