key_grabber: call XResizeWindow when pulling down

[xie-dongping]

In a setting with XMonad and multiple monitors with different resolutions, when pulling down from a smaller monitor, the tilda window size becomes smaller and smaller. This adds a resize function after the call to fix the bug (might be gtk bug, though).

Note that XMonad is not tiling tilda but merely managing it.

Reproduction of the bug:

• Use XMonad as the window manager, set Tilda to floating
• Press the pulldown button the smaller screen which doesn't have tilda
• Expected outcome: tilda pulls down with its original size
• Actual outcome: tilda pulls down with the size proportionally smaller according to the smaller screen.