Various bug fixes & small issues
 --------------------------------

 o RooGaussian

   - Implement getLogVal() to directly calculate the log(Gaussian) - only used
     when RooGaussian is the top-level pdf, or if it is a constraint term


 o RooPoisson

   - Implement getLogVal() to directly calculate the log(Poisson) - only used
     when RooPoisson is the top-level pdf, or if it is a constraint term. Also
     implement approximate log(observed!) term to keep magnitude of
     likelihood small to avoid numeric precision issues


 o RooAbsData, RooDataHist, RooDataSet

    - Implement weightSquared() accessor to return sumW2 value associated with current bin


 o RooAbsRealLValue

    - In inRange() method allow for a small tolerance to avoid numerical precision issues


 o RooChi2Var

    - Allow explicit choice between normal and modified chi-squared calculation through
      DataError() command (RooAbsData::Expected = normal chi^2, RooAbsData::SumW2 is
      modified chi^2). Default is normal chi^2, unless weighted data is supplied, in
      which case SumW2 is selected by default

    - Fix bug in detection of function vs pdf normalization in one of the constructors


 o RooVectorDataStore, RooTreeDataStore

    - Handle new enum type RooAbsData::Expected


 o RooNLLVar

    - Use new RooAbsData::weightSquared() method as cleaner solution to obtained 
      sum-of-weights^2


 o RooAbsPdf

    - In chi2FitTo() pass DataError() argument to createChi2 instead of processing
      it in the fit driver.

    - Fix compiler warnings


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48432 27541ba8-7e3a-0410-8455-c3a389f83636
  Small adjustment in invocation of chi-squared - don't override default arguments


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48433 27541ba8-7e3a-0410-8455-c3a389f83636