Ignore modifier keys only when they are in hanja key list

Ignore modifier keys only when they are in hanja key list

Bug #1036: http://code.google.com/p/ibus/issues/detail?id=1036
If any hanja key has any modifier key, we should ignore that
modifire key, or we cannot make that work.

Let the hanja key 'control + h'.
User may press control, and slightly after press h.
So if we commit preedit string on control key, user will have
no preedit string when he/she press 'h'.

But some case hangul engine need to commit on modifier keys to prevent
client's malfunction which is caused by misimplementation.