git: openjdk/skara: Add Repository::revert

[duke]

Changeset: f57fa464
Author:    Erik Helin <ehelin at openjdk.org>
Date:      2019-08-19 13:44:29 +0000
URL:       https://git.openjdk.java.net/skara/commit/f57fa464

Add Repository::revert

Reviewed-by: rwestberg

! vcs/src/main/java/org/openjdk/skara/vcs/Repository.java
! vcs/src/main/java/org/openjdk/skara/vcs/git/GitRepository.java
! vcs/src/main/java/org/openjdk/skara/vcs/hg/HgRepository.java
! vcs/src/test/java/org/openjdk/skara/vcs/RepositoryTests.java