Possible memory leak WRT on page borders during page generation thread task. about projectzombie HOT 1 OPEN

Did an initial fix of this problem. The problem arises from the fact that in 
PolyVox we have shared blocks. The current method of generating voxels in 
MapGenerator will cause crash (use debugger and watch stack trace) on SetVoxel 
during interleave thread processing. For example, when we generate Voxel(x - 1) 
we will hit the neighboring shared block, and thus under certain conditions 
this will cause a problem because SetVoxel is not thread-safe. 

We mitigate this by generating borders first and at the same set shared blocked 
size to be smaller than 32 blocks, say, 16 blocks. The lower the shared block 
size the lower the probability of two threads hitting the same shared block in 
an unsafe manner. There is of course still possible there will be issues due to 
interleaved threading nature, but the probability is probably very very small 
when the shared block is lower than 32. May want to set shared block size from 
16 to 8 to be more stable, to be more on the safer side of things. 

To completely eliminate this problem we still have to make this thread-safe. We 
can try using atomic variables when writing borders. But let's just go with the 
current solution for awhile and see how stable it is (it's been pretty stable 
so far).