workaround for gtk dnd lockup

[Nerijus Baliunas]

Hello,

it no longer happens with wx 2.8 (still happens with wx 2.6), but this info
could be useful for someone. If you add Option "AllowDeactivateGrabs" "yes"
in Section "ServerFlags" of xorg.conf, you can use Ctrl+Alt+Keypad-Divide
to deactivate any active keyboard and mouse grabs.

Regards,
Nerijus