[Halld-offline] default tracking code

[Simon Taylor]

Hi.

Because of some confusion in recent weeks about the state of the 
tracking code, I would like to announce that the current default track 
fitter
is the SIMD-enabled Kalman Filter (DTrackFitterKalmanSIMD).   For those 
of you who are using 32-bit machines for which the SIMD instructions 
caused crashes, I have implemented a work-around that means you will 
still get the latest Kalman Filter code but without the SIMD 
instructions.   The previous default fitter (ALT1, Dave's global fitter) 
is still available but is no longer under development.  The 
non-SIMD-enabled Kalman filter (DTrackFitterKalman) is deprecated and 
will be removed from the repository shortly.

Simon