This patch fixes http://www.python.org/sf/1668596. If package_dir is '', there is no need to remove package_dir part from data file path names.

I am also attaching 1668596_test.tar.gz. This has the directory I used to test the patch (both on Linux and Windows XP). I will need some more time to come up with a real test case that can be submitted as patch. I am hoping that if there is some one out there who is familiar with distutils test setup, they may be able to come up with a test case quicker than me.