fixed major bug in branch comparison

the old code did a string comparison with == which is obviously wrong.
fixed checkstyle
take the manifest repo itself into account in RevisionState
export our properties to the REST api
Merge pull request #16 from rburgst/fix-comparison

Fix comparison
modifiedFiles may be null
partial fix for JENKINS-17913 expand variables for branch

JENKINS-17913 asked for being able to expand variables for certain
configuration properties I have added expansion for the specified branch
which allows users to choose a branch to checkout and pass it in as a
variable
fixed issue where selecting a branch for manual build no longer worked
fixed check style issues