X11 scroll-wheel improvements

[Eric Wasylishen]

Hey,
I just made two commits to gnustep-back (r34553 and r34554) which make a big 
improvement to scrolling with a mouse scrollwheel or trackpad's scrolling 
feature.

The first helps avoid the GSDisplayServer event queue from filling up which 
prevents window autodisplay, and the second implements coalescing for scroll 
events. The coalescing seems to work very nicely - it means that the rate of 
scroll events sent to gui depends on how quickly gui can deal with them. As a 
result, scrolling with the scroll wheel feels just about as responsive as 
grabbing and moving the scroll bar.

Let me know if it also works well for you, or you have any problems. :-)
-Eric