[Dune] Deprecated methods rbegin/rend

[Oliver Sander]

Dear Dune,
there are deprecated methods rbegin/rend in various place in dune-common
and dune-istl.  They are deprecated because they implemented a non-standard
behavior using a standard name.  I'd like to hear opinions on what should
happen with those methods.  Should we remove them for 2.2?  Or should
we leave them in and reimplement them after 2.2 in a standard-conforming 
was?
--
Oliver