Proof

• New functionality
• Add support for session queuing in the scheduler. This allows to control the number of sessions allowed to process queries concurrently. The feature is enabled by a new parameter 'queue:fifo' in the 'xpd.schedparam' directive. In case of static worker assignment (default, random, round-robin) the max number of running sessions can be limited by another new parameter 'mxrun'; for example
                  xpd.schedparam default mxrun:3 queue:fifo
  will run concurrently only 3 sessions. Additional requests are queued and run as soon as one of the running sessions goes idle. The current policy is FIFO, so that there is a rotation among queued sessions. In the case of load-based worker assignment, the max number of running queries is determined dynamically.
• Add support for repeat functionality in the xrd.worker directive. To avoid repeating the same line N times one can just add 'repeat=N' in the line; for example
                  xpd.worker worker proofwrks:2093 repeat=4
  will define 4 workers on port 2093 of machine 'proofwrks'.
• Fixes
• Fix several problems in TChain::Draw including
• drawing into an existing histogram, i.e. chain->Draw("var>>myhist");
• treatment of histogram merging in case of small statistics, i.e. when
  the autobinning is not or only partially active;
• usage of existing canvases when different histogram names are specified;
  
• Fix a problem causing a duplication of the final feedback object
• Fix problem with determining the subdir name in TFileMerger::MergeRecursive on Windows
• Make sure that the default sandbox is under $HOME/.proof
• Fix a problem with dataset validation in multi-level master setups
• Fix a problem with ordinal numbers in multi-master setups
• Fix a problem with defining the internal paths for executables when configuring with '--prefix'
• Fix backward-incompatibility issue giving the error message  "unknown action code: 5112"