revlog: remove the `_indexfp` method The method is only used two time and we want to move that code to a lower level object. So we simply inline the method to simplify further refactoring.

revlog: avoid opening and closing the file for each cloned revision The previous code was flushing files after each new revision, slowing things down. For exemple, with this change, the evolve repository can run `hg debugupgraderepo --run --optimize re-delta-parent` in about 3.4s instead of 4.5 seconds.

censor: accept censored revision during upgrade They can simply be passed by as censored.

censor: show that censored revision prevent repository upgrade This is not great.

stream-clone: fix a crash when a repo with an empty revlog is cloned

debug-delta-chain: print less data by default This is faster and simpler to read.

debugdeltachain: add a parameter to display all info This will be useful with the next changeset that change the defaul output to display the minimum amount of information.