Created a unit test that reproduces JENKINS-23179
[FIXED JENKINS-23179] git pre-merge fails with matrix project
Removed commented out code
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/main/java/hudson/plugins/git/GitSCM.java
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/test/java/hudson/plugins/git/AbstractGitTestCase.java
Merge remote-tracking branch 'upstream/master'
Merge pull request #235 from galbramc/master

[FIXED JENKINS-23179] git pre-merge fails with matrix project