bind kernel events in Kernel.bind_events

avoids multiple-register of send_input event
remove any lingering raw_inputs on raw_input

There should never be more than one,
so ensure that is the case on creation.

closes #3710
Merge pull request #3716 from minrk/debugagain

raw_input fixes for kernel restarts

- fixes multiple event-registration causing duplicate messages
  after kernel restart.
- removes any raw_inputs hanging around that might have been left by kernel restarts.

closes #3710