manifestv2: set requires at repo creation time
While it should be safe to switch to the new manifest format on an
existing repo, let's keep it simple for now and make the configuration
have any effect only at repo creation time. If the configuration is
enabled then (at repo creation), we add an entry to requires and read
that instead of the configuration from then on.
Check that entry is added to .hg/requires
$ hg --config experimental.manifestv2=True init repo
$ cd repo
$ grep manifestv2 .hg/requires
manifestv2
Set up simple repo
$ echo a > file1
$ echo b > file2
$ echo c > file3
$ hg ci -Aqm 'initial'
$ echo d > file2
$ hg ci -m 'modify file2'
Check that 'hg verify', which uses manifest.readdelta(), works
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
3 files, 2 changesets, 4 total revisions
TODO: Check that manifest revlog is smaller than for v1
$ hg debugindex -m
rev offset length base linkrev nodeid p1 p2
0 0 106 0 0 f6279f9f8b31 000000000000 000000000000
1 106 59 0 1 cd20459b75e6 f6279f9f8b31 000000000000