Fixed misleading tempdir removal error message under Windows.

In my last pull I seem to have missed the fact that td.path is used below for clean-up and also printed when an error might occur, like:

WARNING: Error cleaning up temporaries: remove C:\Users\Nashwan\AppData\Local\Temp/check-867466...
(note the slash before check-...)

This can be very misleading, especially if the error occurs due to an unrelated cause (ex: permission denied), making it seem as though the directory was improperly created in the first place (as was my case).

This fixes the issue, gocheck now displaying a proper error message when it fails to clean-up its temporaries due to outside causes.