Add additional credentials when there is no explicit credential
Log authentication attempts to get a chance to find out the realm.
Fix issue with Subversion Tagging plugin failure.

Now, just make sure you've configured an 'additional credential' for
the repo to tag, and it works.
Simplied code as null check is redundant
Fixed NPE
Merge pull request #70 from daniel-beck/notify-commit-external-credentials

Fix credentials in some use cases
Fix JENKINS-18574
Merge pull request #73 from cbos/master

Fix JENKINS-22199
[JENKINS-21785] Fix for PR 70 / aabd40a
Merge pull request #74 from daniel-beck/notify-commit-external-credentials

[FIXED JENKINS-21785] Check for changes in folders linked via svn:externals fails due to missing credentials

- Typo in original code and externals credentials were not being resolved correctly. Good catch by @daniel-beck
Removed jenkins svnkit in favor of default svnkit library.