hgweb: extract code for emitting multiple changelist records changelistentry() exists so extensions can easily monkeypatch the function to add additional metadata. In at least one case at Mozilla, we have an extension doing this where performance would greatly benefit if we were able to "batch fetch" metadata for all revisions that will eventually have their data set. By extracting the logic for "obtain records for N revisions" into a standalone function, we make it possible for a monkeypatched function to more efficiently bulk fetch data for N revisions. Differential Revision: https://phab.mercurial-scm.org/D3573