• Merge pull request #322 from jlblancoc/fix/planesplit-build-regression
  Fix single-thread build regression: restore two-pass partition in planeSplit()
• Restore two-pass Hoare partition in planeSplit()
  The one-pass three-way partition introduced in 1.9.0 swaps almost every
  element it visits, while the previous two-pass scheme only swaps misplaced
  pairs (about 7x fewer swaps on LiDAR data). This made the single-thread
  KD-tree build 9-12% slower than in 1.8.0.
  The two-pass version is restored over half-open ranges, so it stays safe
  for unsigned Offset types, and keeps comparing coordinates in DistanceType.
  Results are unchanged. A new test exercises heavy ties on the split planes,
  where all three partition regions are populated.
• fix test warnings for ignored return values
• Contributors: Jose Luis Blanco Claraco, Jose Luis Blanco-Claraco