obscache: update the cache key in place Instead of computing the key in place, we update the existing one using the data used for the incremental update of the content. This will help reaching purely incremental cache eventually. The 'getcachekey' function is dropped as it is no longer used.

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