add test for JENKINS-20165
handle SVNEventAction#UPDATE_EXTERNAL

With 1.6 working copy, UPDATE_COMPLETED is not notified with
target path of svn:externals to file.
revert unnecessary newline change at EOF
Merge pull request #56 from yoichi/JENKINS-20165

[FIXED JENKINS-20165] poll externals to file correctly with 1.6 working copy