Improvements in the PROOF tutorials:
     - New tutorial "ntuple", using the selector ProofNtuple.h,.C to the usage of
       TProofOutputFile to merge via temporary files. To run it locally, do

              root[] .L tutorials/proof/runProof.C+
              root[] runProof("ntuple")

       This fills a simple ntuple which saved in the local working directory in the
       file ProofNtuple.root .
       If you run the tutorial using a remote cluster the script will automatically
       start a local xrootd on port 9000 to receive the file.
     - Add methods to ping 'xrootd' or 'xproofd' services at given host:port in getProof.C
       this allows to make consolidate the checks done to setup the tutorial.
     - Explicitely include TDatabasePDG.h in ProofPythia.C to solev a compilation issue
       with recent ROOT versions.


git-svn-id: http://root.cern.ch/svn/root/trunk@29492 27541ba8-7e3a-0410-8455-c3a389f83636