Optimizations:

1) Keep a rectangle updated per-screen rather than regenerate each time
2) Strip palette info when putting pixels into rectangles rather than
   during scaling
3) Tighten up the screen locks a bit
4) Don't require a full resend of both screens on an update request
5) Only force a redraw for cursor movement when the cursor is visible
   (And force it whenever the cursor changes)
6) Avoid doubles in interpolation
7) Heavily optimize interpolate_height()
   interpolate_width() likely doesn't need it because it's generally not
   used and also it reads from the next pixel in memory making the
   prefetchers job easier.
8) Fix some memory-leak-on-error issues
9) For ARGB8 XImages, manipulate the data directly rather than through
   XPutPixel()

At this point, the scaling and X11 output time is heavily dominated by
cache misses.  The only really effective way to reduce this hit is to
spread the work across all the L3 caches in the system or move it into
the GPU.

With the latest updates, at the S...