Extracts the year part of input (yyyy in dd-Mmm-yyyy
       hh:mm:ss.cc).

1  –  Input

       A date.

2  –  Output

       An unsigned integer for years 1858 to 9999.

3  –  Example

       DTR> DECLARE CAL USAGE DATE EDIT_STRING X(23).
       DTR> CAL = "NOW"; PRINT CAL

                 CAL

        1-Feb-1990 08:51:11.55

       DTR> PRINT FN$YEAR (CAL)

         FN$YEAR

              1990

       DTR>