Disable var-length int packing for geometry.

This saves only 0.8% of memory and has a large impact
on spatial index querying performance.
50k nearest edges query on hash-grid:
With var-len int packing: 2564 ms
Without                 : 1844 ms (-30%)

This could be easily re-activated later-on if needed.
Test for negative and positive x in hash grid.
Better map key function in hash grid class.

This prevent some hash collision due to the way the long-hash is computed.

Also inline few small methods used once in the class.