Ensure test functions begin with 'test_' so that the 'testpackage' fixture isn't treated as a test
Add some configuration for test coverage
Ensure that the main copy of ah_bootstrap.py is always used, and that we are returned to the cwd at the end of a test that uses the testpackage fixture
Add the first test that actually tests ah_bootstrap.use_astropy_helpers directly.  Will be adding more tests soon following the same general pattern.
Renamed the testpackage submodule to package_template to make it clearer where this is coming from (likewise rename the testpackage fixture to package_template)
Add global variables to ah_bootstrap for DIST_NAME and PACKAGE_NAME--this is primarily useful for testing ah_boostrap itself with other packages, but it could also be used to make it easy to tweak ah_boostrap for bootstrapping other packages in a similiar manner...
Some slightly improved debug output in ah_bootstrap
Added a new fixture called testpackage (different from the previous fixture of the same name) that creates a very simple package called _astropy_helpers_test_.  It's meant as a stand-in for astropy_helpers itself when testing ah_bootstrap.  Testing ah_bootstrap itself was difficult since by its very nature its purpose is to make things so that astropy_helpers can be imported.  But astropy_helpers is the package under test and is already imported.  We could just use a separate Python interpreter but that makes collecting test coverage data difficult.  So the solution is to use a simpler stand-in for astropy_helpers which is good enough for testing the functionality of ah_bootstrap.
A couple workarounds for issues with distutils--ensure that the distutils log is always reset to its default threshold.  And a workaround for a bug in setuptools...