Fix for EM/em-http-request close_connection

If the em-http-request gem is installed, it will take presidence for the HTTP connection over the EventMachine.  It does not have a .close_connection method, but rather a .close and throws an error when closing an IRC client

See:
camper_van issue #40
https://github.com/zerowidth/camper_van/issues/40

em-http-request
https://github.com/igrigorik/em-http-request/blob/master/lib/em-http/http_connection.rb#L172-201