This fixes a few problems mostly on the server side.

XrdProofdProtocol.h, .cxx
  - Make logging more uniform

XrdProofdResponse.h, .cxx
  - Fix a bug overwriting  the internal stream string and screwing up logging

XrdProofdTrace.h
  - Add macro to differentiate between logging with the stream ID string and
    logging between the general ID string

XrdProofConn.cxx
  - Do not start the garbage collection thread: if any, obsolete physical
    connections are removed when a new (logical) connection is started.


git-svn-id: http://root.cern.ch/svn/root/trunk@18526 27541ba8-7e3a-0410-8455-c3a389f83636