Prefix ivar names with underscore.
-sharedVoxelDataLock is made private through a special category.
Rename GSBlockMesh protocol to GSBlockGeometryGenerating.
Fix bug introduced while making code-style changes.
Change locking scheme in GSChunkGeometryData for the ARC converter.

This is the locking scheme used in
-tryToRebuildSunlightWithNeighborhood:completionHandler:
Add preprocessor conditional to GSOpenGLView to appease the ARC converter.
Change locking scheme in GSChunkGeometryData to appease ARC converter.
Changes to GSActiveRegion to appease the ARC converter.
Changes to GSGrid to appease the ARC converter.
Convert project to ARC.
Use class extensions to define private methods.

- Do not use method names prefixed with underscores.
- Do not use special class categories.
Only use one blank space to separate method implementations.
A few ivars were not prefixed with underscore and were still in header.