Growing the default snapshot buffer size.
Fixing the assert for issue #410. Sometimes it's legit.
Setting replay splitter width wider.
Fixed context size not updating bug.

Fixed a bug in which the size of the canvas was not reset when the playback was reset. This bug is noticeable when a playback calls setContext more than once to change the size of a canvas on a single context: The canvas would erringly not revert to the size at which the context was first created.
Merge pull request #411 from chihuahua/fixContextHeightBug

Fixed context size not updating bug.
Wrote width/height tests for ContextPool.

Made tests for ContextPool more rigorous by ensuring that contexts retrieved have the right dimensions. Also ensured that a new context is not created if one with the same type, attributes, and same canvas dimensions was released earlier.