Forgotten.
Merge branch 'master' of github.com:jenkinsci/git-client-plugin
GitTool configuration moved from git-plugin
[JENKINS-17013] preventive workaround 
warn and return default installation if requested name don't match any registered installation
don't set a default exe so that JGit is use if not explicitly set
implement isCommitInRepo with JGit
implement revParse with JGit
implement hasGitRepo with JGit
implement deleteTag with JGit
implement getTagMessage with JGit
implement clean with JGit
document clean() to both run git-reset + git-clean
delegate to JGit implementation for all supported methods
[JENKINS-17013] use first installation as "default" if no explicit "Default" one exists
getInstallation <-> getDefaultInstallation cycle
fix recursive invocation 
(can't use "this" as delegate)
introduce method to commit, passing author/committer
commit time is set via committer PersonIdent,
so wrap committer to set commit time to current date
implement getTagNames using JGit
explicit possible null value for checkout reference
implement addSubmodule
let checkout() support tag/branch as ref string