Bug fix: Phake_Matchers_Factory::createMatcher('Class_Name') bad behavior

First off, I'm very sorry. In my previous pull request, I made it possible to initialize class names from Phake_Matchers_Factory::createMatcher(). I thought it would be useful, but it turned out to be buggy. PHP:class_implements() works differently from what I thought, it is actually PHP:is_subclass_of() that should have been used.

I fixed that issue, but coming back to the code a second time I noticed that it's an unneeded feature, so I decided to remove the code from Phake_Matchers_Factory::createMatcher(), basically reverting the changes from the last pull request. 

Please review and merge this if you can. I hope no one's lives are ruined by this bug. Sorry!