Fixing unit tests on Travis.

Travis does not use distribute, it uses a recent version of pip (1.5.1
at time of writing) and a recent version of setuptools. Recent
setuptools imports urllib2 from setuptools.compat rather than importing
directly.

Skipping the test on Travis for now.
Merge pull request #43 from ahlmss/fix_unit_tests

Fixing unit tests on Travis.
Merge branch 'master' into reorganise_testing

Conflicts:
	pkglib/tests/unit/test_pyinstall_unit.py
Fixing tests using exec net