Revision 16279

From Anna:
- TFormula::EvalPar() is not changing parameters (the fParams data member) when a user passes his own uparams array as a second argument. Before - sometimes it did, sometimes it didn't.
- TF1::GradientPar() is now 0 on fixed parameters
- TFitter::GetConfidenceIntervals() is now taking the fixed parameters into account
- TLinearFitter::GetConfidenceIntervals()  is now taking the fixed parameters into account
- TLinearFitter::FixParameter() can now be called before a first fit is performed (an accidently found bug :))
- TLinearFitter::Eval() now returns 1 if there are errors in the fit. According changes in:
  --TH1
  --TGraph
  --TGraph2D
  --TMultiGraph