stablerange: compute subranges from parent when possible
Unless we are a merge, we can infer the standard subranges of a range by reusing
the subranger of its parent. We update the implementation to do so.
We still needs the "old way" for merge. We move that code in a dedicated
function for the sake of simplicity.
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes