Bug2038

The first commit fixes documentation so that should be enough to close bug #2038, so please cherrypick at least this one.

The second I had it in half-bad state so I thought I should finish and push it, it doesn't change functionality but allows us to extend splitstring() with the new "append_rest" functionality that I introduced. I changed the interface for RlistFromSplitRegex() but I think it retains compatibility, so even if I missed some old callers where a boolean is passed as the last argument, it shouldn't matter.