revlog: simplify rawtext return value
We're always returning a tuple even though only the raw text is being used,
and we're rebuilding another tuple again higher.
As a bonus, this will remove one tuple creation and deletion
per `raw_text` call, hence fewer gc calls, etc.
Test null revisions (node 0000000000000000000000000000000000000000, aka rev -1)
in various circumstances.
Make an empty repo:
$ hg init a
$ cd a
$ hg files -r 0000000000000000000000000000000000000000
[1]
$ hg files -r .
[1]
Add an empty commit (this makes the changelog refer to a null manifest node):
$ hg commit -m "init" --config ui.allowemptycommit=true
$ hg files -r .
[1]
Strip that empty commit (this makes the changelog file empty, as opposed to missing):
$ hg --config 'extensions.strip=' strip . > /dev/null
$ hg files -r .
[1]