- fix a problem returning the covariance matrix when fit failed. Now all...

- fix a problem returning the covariance matrix when fit failed. Now all minimizer implements CovMatrixStatus() when they calculate the covariance matrix. Add in FitResult method to return covariance matrix status 
- Add a flag in interface of Minimizer::GetMinosError to do separatly positive or negative errors 
- fix usage of  default minimizer from what is defined in etc/system.rootrc

- improve comment in TH1::Fit and TGraph::Fit for usage of TFitResultPtr


git-svn-id: http://root.cern.ch/svn/root/trunk@31604 27541ba8-7e3a-0410-8455-c3a389f83636