[JENKINS-21434] Git Client 1.5.0+ does not resolve reference
repositories correctly (anymore)

- Check for existance of objects directory in reference dir.
- handle bare reference repositories
- replace backslashes with slashes for windows systems
Merge pull request #74 from pauxus/reference-fix

[JENKINS-21434] Git Client 1.5.0+ does not resolve reference
Add MIT license to pom.xml
Merge pull request #75 from vaneyckt/patch-1

Add MIT license to pom.xml
Merge remote-tracking branch 'origin/master' into master-work