perf: add --clear-revlog flag to branchmapload
Having the changelog index already loaded when loading the branchmap can have a
large impact on performance.
Example runs (large private repository):
hg perfbranchmapload -f base
! wall 0.116722 comb 0.120000 user 0.110000 sys 0.010000 (best of 59)
hg perfbranchmapload -f base --clear-revlogs
! wall 0.258246 comb 0.230000 user 0.220000 sys 0.010000 (best of 31)
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).