Bugfix: Minor math bug in AltitudeMap.
Bugfix: Incorrect U/V for ceiling textures in TerrainSystem. Plus, hooks
for detecting seams between floor and ceiling and smoothing lighting
normals between them.
Added catchblock to setRGBA() invocation and implemented toString() to
help debug sparse ArrayIndexOutOfRangeExceptions in Texture.
Bugfix: List may be shorter when get() is invoked in
ThreadManager.gameplay().
Bugfix: Removed pushing null to currentMission in Game as it was
triggering exceptions in behaviors between level loads.
Reduction of flicker and update anomalies in BriefingScreen.