When propagating unsolicited messages, add the possibility to use the message stream ID to
   directly locate the logical connection, instead of scanning all the vector; for PROOF this
   allows to save several useless subcalls.

   After this change you need to do 'make distclean-xrootd' to pick-up the correct version of
   XrdClientConnMgr.hh .



git-svn-id: http://root.cern.ch/svn/root/trunk@24792 27541ba8-7e3a-0410-8455-c3a389f83636