Mouse event rate limit

Hello guys,

recently I had the need to limit the mouse movement event rate because I was using a not-so-powerful machine (namely the all-famous Raspberry Pi). The problem was that in high resolutions, when too many mouse events were piled up, I had to wait for all the bitmap updates to arrive and it took forever. (Using the -mouse-motion was not an option).

The patch I am submitting will add the /mouse-rate:<number> command-line parameter, with rate defaulting to 25. Mouse movement events that are not within that rate will be dropped.

With about 15 events/second I managed to get a pretty decent responsiveness of panning camera / rotating objects on high resolutions (1680x1050 full-screen) on my Pi, using CAD software.

I hope you find it helpful ;)