Sharing test task util method
hop_tasks:branchForDir: better error, support for working dir
GitDir: allow init in non-empty directory
GitDir: new public method runCommand
Git: using process working dir

much less error prone, me thinks
Util: not on parsing windows new lines
Git.parseLsRemoteOutput

helpful
GitDir: parsing local branches correctly...I think...
dart2js plus task running code in harness_browser.html
A lot of git tests
GitDir learned getCommitCount
MapDirectoryPopulator: allow population of non-empty dirs...with flag
Git: better exception details
pretty solid testing for branchForDir

now to start breaking it