Re-add Marc's cet::cbegin and cet::cend.
Re-add Marc's cet::cbegin and cet::cend.

Protect C++2011-isms from GCCXML in case container_algorithms.h is
included by persistent classes.

gartung/fnal-cetlib,gartung/fnal-cetlib,gartung/fnal-cetlib,gartung/fnal-cetlib