stablerange: use sort cache to build 'mergepoint' information Using the walk cache gives use a better complexity we need to scale. There are further improvement we could make, but this is a good first step.

syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
^tests/.*\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
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tests/\.testtimes