Added support for file protocol to SvnClient

This pull request adds support for "file" protocol Svn Urls. Without this patch, the url ends up as " file://:-1/..." and an error is thrown when you attempt to checkout:

        org.tmatesoft.svn.core.SVNException: svn: Unable to open an ra_local session to UR
        svn: Local URL 'file://:-1/....' contains unsupported hostname

I've added a test for the change. Let me know if there are any problems with how I have done this pull request and I'll be happy to fix them