Add an optional argument to TTreeFormula::IsInteger, ie

   virtual Bool_t      IsInteger(Bool_t fast=kTRUE) const;
TTreeFormula::Init calls this function with fast=kFALSE. In this case
the current IsInteger function is executed and the result stored in the kIsInteger bit
of the TTreeFormula. Later when the IsInteger function is called with kTRUE or
no arguments, the function returns immediatly the value of the kIsInteger bit.
This also solves another problem encountered when processing TChains.
It can happen that when TTreePlayer::DrawSelect calls TTreeFormula::IsInteger,
the TBranch objects of the processed Tree are no more available because the last Tree
in the chain has been deleted.


git-svn-id: http://root.cern.ch/svn/root/trunk@18474 27541ba8-7e3a-0410-8455-c3a389f83636