prune: use action "prune", not "touch", in precheck
We have been using "touch" since 06ee4ec88190 (prune: use precheck to
validate revision, 2017-07-23). That commit modified the tests, so it
kind seemed intentional, but I suspect it was still just an oversight.
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
^tests/.*\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes
^docs/training/graphs/
^docs/training/html/
^docs/training/index.html
^docs/training/graphviz-images/
^docs/training/img/
^docs/training/output/
^docs/training/pandocfilters/