Looking at your folder structure, it would appear as though your local copy of piglow.py is interfering with the library.
When it imports Piglow, Python will first look in the current folder and load the piglow.py file instead of the library. The piglow.pyc file is a "compiled" version of this library which Python generates automatically to speed things up.
If piglow.py is a script which you've written, you should rename it to something else so it doesn't conflict.