UV data format usage restrictions

The Gildas UV tables signatures (12 first characters of the binary file) GILDAS_UVDAT and GILDAS_UVSOR are not used anymore⁴. The initialization by GILDAS_NULL sets the generic signature GILDAS_UVFIL instead.

To simplify our life, we have imposed the following constraints

• There must be 7 leading daps before the visibilities. These daps have to be in sequence: code_uvt_u, _v, _w or _scan, _date, _time _anti, _antj. This default ordering of ``mandatory'' daps follows the GILDAS V1 convention.
• The 7 leading daps must be real.
• Usage of Real(8) daps is restricted to code_uvt_ra, code_uvt_dec.