Windows: fall back to current working directory if freetype library not found elsewhere.

Rework the library loading code to allow the freetype dll to be loaded from the current working directory.
Without this for me this binding is useless.

And unless i am completely missing something that comment at the top is wrong about FT_library_filename. Once a value set as a global on one module will not propagate to the other. Even if that were the case the value would get overwritten before its ever checked.
Any reason not to use os.path.join ?