o (LoadTree) We no longer delete clones from the trees in
       the chain, those trees still need to be able to synchronize
       their clones' branch addresses.  We now copy the chain's
       clone list into the newly fetched tree's clone list because
       it is the tree's destructor (which is called when we switch
       to the next file in the chain) that is responsible for
       resetting the addresses of the branches of the clone trees.
       If this is not done, the branches of the clone trees will
       be pointing at memory which was deallocated when the master
       tree was destroyed at the file switch.

     o (Merge) Improve documentation.


git-svn-id: http://root.cern.ch/svn/root/trunk@15795 27541ba8-7e3a-0410-8455-c3a389f83636