Added fix for Issue#977

I have added the fix for python setup.py build_sphinx failure for Python 3.x pathname2url ImportError.

Note the import error has now disappeared, but there are other Python 3.x
incompatibilities present:
 1. No member attribute decode in str
 2. str doesn't support buffer interface in Python3
 3. unicode encoding in this way u'...' is no longer permitted
 4?.....

I believe the code needs to be examined thoroughly to make it suitable for
Python 3.x