#15 Multiple Append calls cause OutOfMemory exception

[Craig Andera]

Scrolling unit test causes "out of memory" error
* Appears to be fixable by disabling double buffer.
Yuck. Find better solution.
* Refactored unit tests to avoid the problem, but
this is not acceptable.

Current guess: it has something to do with the resource
acquisition done during layout. Isolate this, and/or
update BeginUpdate/EndUpdate to suspend layout while
updating.