calloc. Since we copy the first 1/1.3 part of the new array from the
existing nodes, only the rest 0.3/1.3 should be initialized to zero.
This should in theory cut down the times of occasional hangs with
dyntopo, since my guess is that it is caused by dynamic reallocations.
Maybe a linked list structure would help here? This is a bigger change
though, leaving as is for now.
Also, minor cleanup, delete duplicate ghash deletion and remove unneeded
commented code.
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