Synergy patch

Synergy has a nasty bug where if you switch screens with a hotkey, then switch again with the mouse, the hotkey modifier key gets stuck in the down state. I submitted a patch a few years ago, but it never got integrated since the project wasn't being maintained. Synergy has now been resurrected and merged with Synergy+, and the bug still exists. Here's the patch (which will need some tweaking for the new codebase).