Merge commit '7fde2daeed593684120d75de07598154f3ddaf2c' as 'ast'

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diff --git a/ast/pal/palFk54z.c b/ast/pal/palFk54z.c
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+/*
+*+
+*  Name:
+*     palFk54z
+
+*  Purpose:
+*     Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
+*     zero proper motion and parallax.
+
+*  Language:
+*     Starlink ANSI C
+
+*  Type of Module:
+*     Library routine
+
+*  Invocation:
+*     palFk54z( double r2000, double d2000, double bepoch, double *r1950,
+*               double *d1950, double *dr1950, double *dd1950 )
+
+*  Arguments:
+*     r2000 = double (Given)
+*        J2000.0 FK5 RA (radians).
+*     d2000 = double (Given)
+*        J2000.0 FK5 Dec (radians).
+*     bepoch = double (Given)
+*         Besselian epoch (e.g. 1950.0).
+*     r1950 = double * (Returned)
+*        B1950 FK4 RA (radians) at epoch "bepoch".
+*     d1950 = double * (Returned)
+*        B1950 FK4 Dec (radians) at epoch "bepoch".
+*     dr1950 = double * (Returned)
+*        B1950 FK4 proper motion (RA) (radians/trop.yr)).
+*     dr1950 = double * (Returned)
+*        B1950 FK4 proper motion (Dec) (radians/trop.yr)).
+
+*  Description:
+*     This function converts star positions from the IAU 1976,
+*     FK5, Fricke system to the Bessel-Newcomb, FK4 system.
+
+*  Notes:
+*     - The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.
+*     - Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
+*     only is provided for.  Conversions involving other epochs will
+*     require use of the appropriate precession functions before and
+*     after this function is called.
+*     - The FK5 proper motions, the parallax and the radial velocity
+*      are presumed zero.
+*     - It is the intention that FK5 should be a close approximation
+*     to an inertial frame, so that distant objects have zero proper
+*     motion;  such objects have (in general) non-zero proper motion
+*     in FK4, and this function returns those fictitious proper
+*     motions.
+*     - The position returned by this function is in the B1950
+*     reference frame but at Besselian epoch BEPOCH.  For comparison
+*     with catalogues the "bepoch" argument will frequently be 1950.0.
+
+*  Authors:
+*     PTW: Pat Wallace (STFC)
+*     DSB: David Berry (JAC, Hawaii)
+*     {enter_new_authors_here}
+
+*  History:
+*     2012-02-13 (DSB):
+*        Initial version with documentation taken from Fortran SLA
+*        Adapted with permission from the Fortran SLALIB library.
+*     {enter_further_changes_here}
+
+*  Copyright:
+*     Copyright (C) 1995 Rutherford Appleton Laboratory
+*     Copyright (C) 2012 Science and Technology Facilities Council.
+*     All Rights Reserved.
+
+*  Licence:
+*     This program is free software: you can redistribute it and/or
+*     modify it under the terms of the GNU Lesser General Public
+*     License as published by the Free Software Foundation, either
+*     version 3 of the License, or (at your option) any later
+*     version.
+*
+*     This program is distributed in the hope that it will be useful,
+*     but WITHOUT ANY WARRANTY; without even the implied warranty of
+*     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*     GNU Lesser General Public License for more details.
+*
+*     You should have received a copy of the GNU Lesser General
+*     License along with this program.  If not, see
+*     <http://www.gnu.org/licenses/>.
+
+*  Bugs:
+*     {note_any_bugs_here}
+*-
+*/
+
+#include "pal.h"
+#include "pal1sofa.h"
+
+void palFk54z( double r2000, double d2000, double bepoch, double *r1950,
+               double *d1950, double *dr1950, double *dd1950 ){
+
+/* Local Variables: */
+   double r, d, px, rv, y;
+
+/* FK5 equinox J2000 (any epoch) to FK4 equinox B1950 epoch B1950. */
+   palFk524( r2000, d2000, 0.0, 0.0, 0.0, 0.0, &r, &d, dr1950, dd1950,
+             &px, &rv );
+
+/* Fictitious proper motion to epoch "bepoch". */
+   y = bepoch - 1950.0;
+   *r1950 = r + *dr1950*y;
+   *d1950 = d + *dd1950*y;
+
+}
+