Insane Border Support: Do NOT use lookup table with large border strengths. This saves both memory and time.
Insane Border Support: fix floating point error with xbord 0 ybord 675.
Minor refinement:
1) use size::size_t instead of int so that insane block size is possible in 64-bit build
2) do not crash in side xy_malloc
Keep track of memory size allocated by xy_malloc
Add lot of log and auto shrink
Add reg option max_cache_size_mb (negative for auto, which would be half of physical memory size but never exceed 2G in 32-bit build)