BUG : fix eps corruption when using clipping

_get_clip_path was returning '<built-in function id>' instead
of the ps-function name like it should have been.  This was introduced
in 9b9c0c6fbdd53ec42e2a1edecc9c6895b6f7a3ef in PR #2927.

Closes #3523
didn't the PEP8 tool notice this? I know pylint would have warned about namespace collisions. Then again, I guess it isn't really a collision as much as a typo.