Don't double numpad keys in SDL tiles.

We were getting both the keydown event for KP_2, and if numlock was
enabled a textinput event for "2".  Use a hack (stopping and restarting
text input---it works here) to suppress the textinput event when we
are already going to handle the keydown.

This likely screws up some input methods.
Treat keypad . as delete in SDL.

No other numpad key still cared about the numlock state.  And having
'.' on numpad isn't that helpful when KP_5 does that already.

The key is currently unbound.