Paint and mouse events are coalesced in the event queue currently.
However, the intermediate step of posting them to the PostEventQueue in
/sun/awt/SunToolkit.java produces a noticeable performance hit.

This was done very artificially: as a test case, Robi simply changed
every place where the event was posted to the PostEventQueue to post
directly to the EventQueue. Painting appeared to happen much faster
when this was done.

We should investigate where the slowdown is, and what we can do about it.
For example, adding code to the PostEventQueue to do coalescing of paint
events might be one approach. Or, it might turn out that the bottleneck
lies somewhere else.