log: use revsetlang.formatspec() thoroughly
This patch replaces %(val)s and %(val)r with %r (expression) and %s (string)
respectively. _matchfiles() is the exception as it takes a list of string
parameters.
"--prune REV" could take a revset expression if it were "ancestors(%(val)s)",
but this patch doesn't change the existing behavior.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).