[Integrated] RFR: vcs: add Hash::zero

[Erik Helin]

Changeset: b090b57c
Author:    Erik Helin <ehelin at openjdk.org>
Date:      2020-02-24 14:14:32 +0000
URL:       https://git.openjdk.java.net/skara/commit/b090b57c

vcs: add Hash::zero

Reviewed-by: rwestberg

! forge/src/test/java/org/openjdk/skara/forge/CheckBuilderTests.java
! jcheck/src/test/java/org/openjdk/skara/jcheck/BinaryCheckTests.java
! jcheck/src/test/java/org/openjdk/skara/jcheck/ExecutableCheckTests.java
! jcheck/src/test/java/org/openjdk/skara/jcheck/HgTagCommitCheckTests.java
! jcheck/src/test/java/org/openjdk/skara/jcheck/WhitespaceCheckTests.java
! vcs/src/main/java/org/openjdk/skara/vcs/CommitMetadata.java
! vcs/src/main/java/org/openjdk/skara/vcs/Hash.java
! vcs/src/main/java/org/openjdk/skara/vcs/Patch.java
! vcs/src/main/java/org/openjdk/skara/vcs/git/GitCommitMetadata.java
! vcs/src/main/java/org/openjdk/skara/vcs/hg/HgRepository.java
! vcs/src/main/java/org/openjdk/skara/vcs/openjdk/convert/GitToHgConverter.java
! vcs/src/main/java/org/openjdk/skara/vcs/openjdk/convert/HgToGitConverter.java
! vcs/src/test/java/org/openjdk/skara/vcs/RepositoryTests.java