Buitlin `input` doesn't work over zmq

[fperez]

Typing into any client with a remote kernel:

input('a')

produces

---------------------------------------------------------------------------
EOFError                                  Traceback (most recent call last)
<ipython-input-3-138401a29eba> in <module>()
----> 1 input('a')

EOFError: EOF when reading a line

a

This should be a simple matter of handling input calls just like we do raw_input, since in the end they are both doing the same stdin.read().