Summary:
This adds a command for producing tree manifests for existing manifests in the
repository. The tree manifests are stored similar to how vanilla mercurial
stores them, but the root revs are in 00manifestree.i instead of 00manifest.i
and we fake the root node to be the same as the flat manifest node, so we can
reference either the flat or the tree easily.
Test Plan: Added a test. Also began converting fbsource
Reviewers: #mercurial, simonfar
Reviewed By: simonfar
Subscribers: stash, mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D4092252
Signature: t1:4092252:1478260394:a55360a8ba83ad85b1694cb93f0788f1f672ef61
