stablerange: introduce a smarte version of stablerange for 'mergepoint' This implementation will using caching and smarter algorithm based on these cache. For now it inherit most of it code from the dummy version for convenience. The inheritance to the dummy version should be dropped eventually.

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