Utility plugin for Git-related support

Extracted from git-plugin to make it easier for other plugins to use and contribute new features.

see Jenkins wiki for detailed feature descriptions
use JIRA to report issues / feature requests

Contributing to the Plugin

Refer to contributing to the plugin for suggestions to speed the acceptance of your contributions to the git client plugin.

To Do

Fix bugs
Create infrastructure to detect files opened during a unit test and left open at exit from test
Create credential tests
Create submodule tests
Improve code coverage in current tests
Improve javadoc
Complete more of the JGit implementation