Development: SetDesktopSize Cleanup

Right now the SetDesktopSize call (and equivalents from X11) are causing multiple ExtendedDesktopSize to be emitted to the client, even though one would be sufficient. This is not currently a practical problem, but it is inefficient and might cause problems down the road.

The call chain shown below describes the flow of calls when we get either a SetDesktopSize from a VNC client, or when a X11 client uses RandR. If you follow the calls, you'll notice that we end up in writeExtendedDesktopSize() multiple times. We need to figure out an architecture that avoids this problem.

SetDesktopSize                          X11
|   |                                  /|
|   | 1                               / |
|   |                                 | |
|   \-> setScreenLayout()             | \-> ??()
|       |     |                       |     |
| 2     | 1   \-----------------------+-----\-> setScreenLayout()
|       |                             |         |
|       \-> RRSetConfig()             |         \-> screenLayoutChanged()
|           |                         |                       |
|           \-> vncRandRSetConfig() <-/                       |
|               |                                             |
|               \-> setFrameBuffer()                          |
|                   |                                         |
|                   \-> setPB()                               |
|                       |                                     |
|                       \-> pixelBufferChanged()              |
|                           |                                 |
\---------------------------\-> writeExtendedDesktopSize()<---/