Lua: Various improvements

Some stuff requested by R00Kie.
To be more specific, it stopped me from being able to test the IncludeScript changes past the initial map load, like so:

```lua
	includescript = function(player)
		IncludeScript("subdir/test")
		assert_equal( subdir_file_loaded, true )
		subdir_file_loaded = nil
		IncludeScript("subdir\\test")
		assert_equal( subdir_file_loaded, true )
	end
```