obshistory: only display each revision once in debugobshistory When using a revision range, the same precursor could have been displayed more than once. Use a cache to display each revision only once. It's a fix until we found the nicest way to display obs history.

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