Merge branch 'nd/shallow-fixup' into maint

Code cleanup in shallow boundary computation. * nd/shallow-fixup: shallow.c: remove useless code shallow.c: bit manipulation tweaks shallow.c: avoid theoretical pointer wrap-around shallow.c: make paint_alloc slightly more robust shallow.c: stop abusing COMMIT_SLAB_SIZE for paint_info's memory pools shallow.c: rename fields in paint_info to better express their purposes