upgradegeneraldelta: update to work with upstream revlog changes
Upstream mercurial commit ac6446611ad2 changed revlog.versionformat from a
string to a struct.Struct object. The upgradegeneraldelta extension needs to
be updated to deal with this.
Confirmed existing tests pass, and manually tested using pull with
upgradegeneraldelta enabled. I believe this extension shouldn't really be in
use in any repositories any more, but somehow some users did run into this.
Reviewers: #fbhgext, sid0
Reviewed By: #fbhgext, sid0
Differential Revision: https://phab.mercurial-scm.org/D162