Adjusted help for 'branches' param

...to latest changes in git-client plugin.
https://github.com/jenkinsci/git-client-plugin/pull/135
Merge pull request #244 from alexanderlink/git-client-PR135-docu

Adjusted help for 'branches' param
Fixing expected GIT_BRANCH environment variable behaviour

See comments in https://github.com/jenkinsci/git-plugin/pull/225
Extracted getBranchName method - needed at 2nd location
Added branchSpec SCMTrigger behaviour tests
Added JGit and CliGit SCMTrigger tests
Added SCMTrigger tests with disabledRemotePolling
Speeding up SCMTrigger tests
Merge pull request #232 from alexanderlink/branchSpecSCMTriggerTests

SCMTrigger tests for various branch specs
Update joda-time to 2.4
Use git-client 1.10.1, first version to include CheckoutCommand.timeout()
Add timeout as a checkout option
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/test/java/hudson/plugins/git/AbstractGitTestCase.java
Merge branch 'master' into custom