Use ast_free() instead of free(), pointed out by eliel on IRC.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@161350 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_voicemail.c

@@ -10126,7 +10126,7 @@ static char *substitute_escapes(const char *value)
 	}
 
 	result = ast_strdup(str->str);
-	free(str);
+	ast_free(str);
 
 	return result;
 }