refs #476. Merged visitor branch into trunk. Used 'svn merge /branches/visitor' because --reintegrate did (currently) not work on our repo. Since I could not merge as suggested in subversion manual, I reverted all mergeinfo properties to avoid future confusion by svn-client. This means (I think) that there will be no connection about this commit and the visitor branch, but to svn-client this will look like a large changeset (just like a merge in the old days).