coverage.py can't find source file

[Follower]

> some of the files can't be found because they are not in the same directory as 
> configure.py and unit_test.py.  But only SOME of them.
I believe there is a known issue with utilities that make use of .pyc
files (such as coverage tools) relating to the use of non-absolute
file paths.

The file path that gets stored as the "__file__" attribute is a
relative path, as a result, if an attempt is made to locate the source
file it will fail if the current directory is different to the current
directory when the .pyc file was created.

--Phil.