Change type of SocketEngine::CurrentSetSize to size_t from int
New socketengine stuff:

Use vectors that grow as necessary instead of mass allocating everything at once
Rework poll engine logic to make sense
Coding style changes in socketengines
Fix oversight in 3752b3f59d5216d7dc6221a361efc76b9ad2273d
socketengine_epoll Remove needless initialization of epoll_event when removing an fd
socketengine_kqueue Remove dead code