Nosetests cannot find tests inside eggs

[tovrstra]

This may have been reported before: #567, #250, #41 However, these bug reports are very old and the problem still exists, even though it is mentioned in some that it is solved.

Steps to reproduce the problem:

1. Either install nosetests 1.3.7 or the latest version from github (7c26ad1e6b7d308cafa328ad34736d34028c122a at the time of writing).
2. Clone the following simple project: https://github.com/theochem/derivcheck
3. Comment out the zip_safe=False line from setup.py, as to let it install as an .egg file.
4. Run python setup.py install --user (or install in a virtualenv).
5. Change to your home dir: cd, i.e. move away from the source tree.
6. nosetests derivcheck.

I get this output:

----------------------------------------------------------------------
Ran 0 tests in 0.082s

OK

I was expecting this output, obtained with zip_safe=False:

..............................
----------------------------------------------------------------------
Ran 30 tests in 0.669s

OK