This routine is called by FTx_FITTER to fit each event in turn. If necessary it has to create the FT dispatch bank. It performs the fitting ignoring any hit that has the discard bit set in the PF (PMT Flags) bank. Depending on the fitter method, it may drop additional hits, and if so sets a bit specifically reserved for the fit method in the PF bank. On completion, it stores its results in an FTx/FTxV/FTxT (Summary/Vertex/Track) subtree. The FTxT is only present if the fitter has the ability to give a track direction.