Revision 33781

   - Optimize the validation step in the case not all the entries are required.
     The validation step is stopped as soon as the requested number of events is reached.
     If the parameter "PROOF_ValidateByFile" is set to 1, the number of files is exactly what
     needed; otherwise the number of files may exceed the number of fles needed by #workers-1
     (this is the default because additional, serial, checks are needed to ensure that only
      the files really required are open).
     This feature was requested in the context of ALICE reconstruction.
     This new feature is used as an example in the "eventproc" tutorial in runProof.C .
   - The patch also fixes a subtle bug affecting the (possibly rare) case when not all entries
     are required and # entries does not correspond to an complete subset of files (e.g.
     # entries = 1001000 with files of 100000 entries each). The effect was uncomplete
     processing (skipped events, magenta bar) or a session freeze.