KScreenlocker tries to clear the clipboard on load. However, klipper
also (by default) automatically keeps the last relevant item in the
clipboard. Whilst both parts work correctly, Plasma as a whole does not.
This became a problem when we added the reveal password button as it is
a data leak.
MF doesn't want an X specific fix, which is fair enough. My earlier
patch removing the reveal button was blocked, which is fair enough.
That doesn't leave many nice places, but we do need to do something.
This patch intercepts the paste shortcut at the window level.
Doing it at a theme level doesn't easily work with QQC1 as the child
gets key events first. With QQC2 it probably whould, but PC3 doesn't
have the reveal button.