Add U_s parameter for HMSFRs to kdist calculation

Add the U_s parameter from the Reid et al. (2014) rotation curve to the
kinematic distance computation.  This introduces a change of at most 0.2 kpc
in the derived heliocentric distance to objects, and in most places it is much
smaller.  This was added in response to a referee comment.

	modified:   conffiles/galactic_params.conf
	modified:   rot_curve/omni_vphys2vlsr.pro
	modified:   subroutines/omni_read_conffile_galactic.pro