Add new fitting functions in TProofBench draw

  Scalability for multicores with hyperthread enabled shows a shape with a kink corresponding
  to the transition from the 'real core' to 'hyperthread core' regime. The available functions
  used to model scalability can be modified to include this effect in the simplest way.
  A new fit option has been added to TProofBench::DrawCPU and TProofBench::DrawDatSet, with the
  possibility to indicate the number of real and hyperthreaded cores.
   Derive TSelectorList from THashList instead of TList

   The same sort of lookup problem recently fixed by
        http://root.cern.ch/gitweb?p=root.git;a=commit;h=83f0b8fbb3ab3664b7026ee7b7fd3b70b91261c7
   (in TDirectoryFile)
   affects also merging in memory in PROOF, essentially because the selector outputlist (class TSelectorList)
   is a TList and needs to be looked up by name a certain number of times. This patch reduces
   the impact of lookups by deriving TSelectorList from THashList.

   Follows a private report from Alexander Mann from ATLAS/Munich .
Prevent a buffer overflow