Introduce two new major optimizations for the Tree cache.

  -in case of a TChain, the list of branches computed during the
   training phase of the first file is reused for all the other files.

 -add support for TEventlist. Only the baskets referenced by the list
  are added to the cache. This has requested a new function in TEventlist
    Bool_t TEventList::ContainsRange(Long64_t entrymin, Long64_t entrymax)
       // Return TRUE if list contains entries from entrymin to entrymax included.


git-svn-id: http://root.cern.ch/svn/root/trunk@15455 27541ba8-7e3a-0410-8455-c3a389f83636