transactions: convert changes['phases'] to list of ranges
Consecutive revisions are often in the same phase, especially public
revisions. This means that a dictionary keyed by the revision for the
phase transitions is highly redundant. Build a list of (range, (old,
new)) entries instead and aggressively merge ranges with the same
transition. For the test case in issue5691, this reduces memory use by
~20MB.
Differential Revision: https://phab.mercurial-scm.org/D8125
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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
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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).