Merge pull request #1634 from minrk/proxylauncher Incremental improvements to SSH launchers: * add to_send/fetch steps for moving connection files around. * add SSHProxyEngineSetLauncher, for invoking to `ipcluster engines` on a remote host. This can be used to start a set of engines via PBS/SGE/MPI *remotely*. This makes the SSHLauncher usable on machines without shared filesystems. When sending files, the destination directory must *already exist* - that is, `ipython profile create` may be necessary on the remote system, before the security dir exists for putting the connection file the first time.