Improve performance of reading a branch with an std::list<int> by 25%
by migrating to using the StreamerInfoAction and by implementing
the access to iterator (creation, copy, increment, delete) via
template function (rather than reallying on the slow mechanism
using 'At' (and its use of the fEnv) ...)


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48943 27541ba8-7e3a-0410-8455-c3a389f83636