Perf fixes june 2014 2

I replaced VOXELFLAG_NOT_LOADED and VOXELFLAG_INEXISTENT by VOXELFLAG_NO_DATA, the only one using first one was addArea and there it's been used for "performance optimization" sadly that one resulted in exactly opposite because of not being able to use memcpy for copying data. New variant may copy a little bit more data but the overall performance is still way better then before.
There's one situation where new one might be slower, create a voxelmanip with a few loaded nodes in lower left and upper right corner and a huge distance in between. Still this scenario most likely will fail anyway. usually this is not how voxelmanip is used, and regular usage is way faster then before.