templater: add strip function with chars as an extra argument This allows specifying characters to strip, like the Python strip function.

Merge with main.

revlog: add exception when linkrev == nullrev When we deployed the latest crew mercurial to our users, a few of them had issues where a filelog would have an entry with a -1 linkrev. This caused operations like rebase and amend to create a bundle containing the entire repository, which took a long time. I don't know what the issue is, but adding this check should prevent repos from getting in this state, and should help us pinpoint the issue next time it happens.

merge with stable