After much tinkering and tweaking adding revision support, and making compatible changes to User Revision, this is a beta version-2 release with a lot of code changes. Most significant are:
Addition of revisions, in the same style as node revisions.
Consistent with the 2.x release of User Revisions, so that using both offers a consistent UI.
Addition of profile2_diff as a sub-module. This depends on, and integrates with, the main Diff module, adding a new settings sub-tab under the Entities tab of Diff configuration.