fix http push 401

Some git clients(eclipse egit, some git version..) report `http 401, rpc failed` and don't ask user for username & password if server return true on `GET /myrepo.git/info/refs?service=git-receive-pack` but false on `POST /myrepo.git/git-receive-pack`. 

This cause git client do `Counting objects` first and then ask you for username & password or report `http 401, rpc failed`.  Ask username  & password first is better?