drophack: major speedup to marker stripping
It appear that each call to obsstore.add have a significant overhead (in
particular the creation of a set form the list of markers and file system
operation to the obsstore file.
We now compute the marker we need to store and write them in a single call.
syntax: re
/figures/[^/]+\.png$
^docs/build/
^docs/html/
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$