added astropy_helpers branch of package-template as a submodule in astropy_helpers.tests--this will allow us to use the package template itself as our test project for testing astropy_helpers :)
Make astropy_helpers.tests into a proper subpackage, but exclude it from sdists to keep those small.  Running the astropy_helpers tests should be of interest to developers only for now.  Also make sure the testpackage isn't recursed into for py.test since we don't want to run *its* tests
Add our first test of astropy_helpers--this test actually helped catch a bug which was fixed in c3f841b9e099f506a751b8a6971b15e7e3d6590a