Change data.py so flag_richardson==False prints out a negative value for the tolerance for Fortran code...
Eventually need to update flagging routines to include this as in 2d
changed flag2refine tolerance in euler_3d_radial.  Note that results do not look completely symmetric -- need to debug further?
Merge pull request #81 from rjleveque/fix_3d_flag_richardson

Fix 3d flag richardson