Merge pull request #1315 from yogo1212/http_per_socket_bebcb

In it's current form, libevent requires multiple struct evhttp objects to be created in order to enable listening on sockets with more than one type of encryption.

This change allows specifying per-socket how the associated bufferevents should be created.
Thus, it becomes possible to have multiple listening sockets with different encryption parameters using only one evttp.