use ROUTER/DEALER sockets for stdin...
use ROUTER/DEALER sockets for stdin
stdin requests are now directed to the frontend that made the execution
request that called raw_input.
allow_stdin flag added to execution_request to indicate whether stdin_requests are allowed.
StdInNotImplementedError exception class added to IPython.core.error, and is raised if raw_input is called from execute requests where allow_input is undefined.
closes gh-673
