ENH: BRAINSFit fixes for making backwards compatible

Slicer operations that succeeded before are not taking a very long time
and this patch attempts to address that.
PERF: Set better default behavior for BRAINSFit

Several of the BRAINSFit default behaviors were causing
extreme processing to occur.  For example, a convergence
threashold of 0.0 was set (meaning that perfect convergence was
needed in order to abort processing).