SLA_DCS2C - Spherical to Cartesian

ACTION:
     Spherical coordinates to Cartesian coordinates (double precision).
CALL:
     CALL sla_DCS2C (A, B, V)

GIVEN:

      A,B D spherical coordinates in radians: alpha, delta etc.

RETURNED:

      V D(3) x,y,z unit vector

NOTE:
     The spherical coordinates are longitude (+ve anticlockwise looking from
     the +ve latitude pole) and latitude. The Cartesian coordinates are
     right handed, with the x-axis at zero longitude and latitude, and the
     z-axis at the +ve latitude pole.