Fix tests using virtualenv on Windows.

Do not hard code bin as the location of the executables, as this is not
correct on Windows.
better messages when requirements aren't met for "pip wheel"
fix wheel test to match current error message
Update requests to 2.0.1
Remove license for no longer bundled software
Merge pull request #1256 from dstufft/update-requests

Update requests to 2.0.1
Merge pull request #1254 from pfmoore/win-tests

Fix tests using virtualenv on Windows.