Add git branch command.
Add git checkout command.
Add git push command.
Add git commit command.
Add merge support in git.
More work on merge trees.
Merge branch 'master' into git_branch
minor fixes.
Add git pull command.
Add git conditions class.
Merge branch 'master' into git_commands
Add dart doc, addressed other comments.
Move GitOptions class to separate file.
Add placeholder for git commands tests.
Fix broken objectstore test.
Fixed typo.
Merge pull request #317 from dart-lang/git_commands

Git commands