catch no .gitconfig when git:remote is called

This commit addresses issue #536

The fix is compatible with Ruby 1.8 and 1.9. 

I wrote a corresponding test, but it needs refactoring.  I'm new to mocks/stubs, as well as writing a test which relies on the tester's system. It doesn't seem right to be renaming the tester's gitconfig, but it does what it should.