Bug fix, after irc report sk1p:

frame-sliding (LMB) in action, nla, sound and ipo window went into very
tight while loop, causing cpu to choke. Added nice idle.

Bug fix, found self while testing:
- relative.blend, editmode
- delete part, exit editmode
- enter editmode, undo twice, exit editmode -> crash

The trick to copy 'old' locations of vertices to keys isnt undo-resistant
yet. This fix at least doesnt crash, but copying doesnt work when undo-ing
back to previous editmode session (indices just differ from current mesh...)

source/blender/src/space.c

@@ -1797,6 +1797,7 @@ static void winqreadipospace(ScrArea *sa, void *spacedata, BWinEvent *evt)
 						update_for_newframe();
 						force_draw_all(0); /* To make constraint sliders redraw */
 					}
+					else PIL_sleep_ms(30);
 				
 				} while(get_mbut() & mousebut);
 			}