Couple of changes in preparation for 'm' safety:

- auto formatting
- add gc control to ffi
- add gc_guard to util functions
- use gc_guard to make util error handling functions never trigger __gc
  metamethod Lua errors even without __gc metatable wrapper
- sort of a technicality, don't call luaL_requiref outside of the Lua
  constructor, as it could trigger the garbage collector when user code has had
  a chance to set __gc metamethods.  Changes the API to load the debug table.

src/tests.rs

@@ -15,12 +15,8 @@ fn test_load() {
 }
 
 #[test]
-fn test_load_debug() {
-    let lua = Lua::new();
-    lua.exec::<()>("assert(debug == nil)", None).unwrap();
-    unsafe {
-        lua.load_debug();
-    }
+fn test_debug() {
+    let lua = unsafe { Lua::new_with_debug() };
     match lua.eval("debug", None).unwrap() {
         Value::Table(_) => {}
         val => panic!("Expected table for debug library, got {:#?}", val),