Summary:
Ref T11823. Currently, we have a "RefCursor" table which stores rows like `<branch or tag name, commit it is pointing at>` with some more data.
Because Mercurial can have a single branch pointing at several different places, this table must allow multiple rows with the same branch or tag name.
Among other things, this means there isn't a single PHID which can be used to identify a branch name in a stable way. However, we have several UIs where we want to be able to do this.
Some specific examples where we run into trouble: in Mercurial, if there are 5 heads for "default", that means there are 5 phids. And currently, if someone deletes a branch, we lose the PHID for it. Instead, we'd rather retain it so the whole world doesn't break if you accidentally delete a branch and then fix it a little later.
(I'll likely hold this until the rest of the logic is fleshed out a little more in followup changes.)
Test Plan: Ran `bin/storage upgrade`, saw the table get created without warnings.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T11823
Differential Revision: https://secure.phabricator.com/D18602
