Allow failed/delayed/mocked resource URLs to be specified with RegExps

While trying to use the mock/delay/fail APIs with socket.io 1.x clients I found it difficult, because the URLs that are generated change each time.  For example, /socket.io-1.x/?EIO=3&transport=polling&t=1417012813261-0

This pull request adds the ability to match mocks/delay/fail handlers with a RegExp instead of just fixed strings.