Convert Julian day and seconds into a time string

INTERFACE:

    subroutine write_time_string(jul,secs,timestr)

DESCRIPTION:

Formats Julian day and seconds of that day to a nice looking character string.

USES:

    IMPLICIT NONE

INPUT PARAMETERS:

    integer, intent(in)                 :: jul,secs

OUTPUT PARAMETERS:

    character(len=19)                   :: timestr

REVISION HISTORY:

    Original author(s): Karsten Bolding & Hans Burchard