Better part path lookup.

Includes everything mentioned in https://github.com/le717/LDR-Importer/issues/40#issuecomment-31278726 , and uses (a slightly modified version) of the code from https://github.com/le717/LDR-Importer/issues/40#issuecomment-31279788

NEEDS TO BE TESTED ON WINDOWS AND OSX.
It should work perfectly fine on OSX, not so sure about windows.