[WIP] Feature/fix libmproxy 1269

Issue #1269 

 - [x] spiderman works with libmproxy
 - [x] localproxy works with libmproxy
 - [x] sqlmap works with libproxy
 - [ ] Add more unittests for Proxy and w3afHandler
Have you tried to translate these lines into the [requirements.py](https://github.com/andresriancho/w3af/blob/feature/fix_libmproxy_1269/w3af/core/controllers/dependency_check/requirements.py#L45) file? Adding them there should be enough to have circle install them.