Ticket #3225: first Backspace/Delete ignored after mouse click in an input widget.

Initial commit: WInput: refactoring of text marking.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(input_event): fix handling of first mouse click.
Merge branch '3225_input_bs_del_after_mouse_click'

* 3225_input_bs_del_after_mouse_click:
  (input_event): fix handling of first mouse click.
  Ticket #3225: first Backspace/Delete ignored after mouse click in an input widget.