make 'groff' depend on 'ghostscript'

[Bjarni Ingi Gislason]

  1) to get the URW-fonts

  2) to avoid people having to ask on a groff-list

  3) to elevate status of 'ghostscript' from 'recommends' to
'depends' (Debian)

  4) the configure script already asks about it

  5) groff's default output is PostScript.

  6) the packet 'groff' produces some 'ps' files, like (in Debian
/usr/share/doc/groff):

./examples/hdtbl/col_rowspan_colors.ps.gz
./examples/hdtbl/fonts_x.ps.gz
./examples/hdtbl/fonts_n.ps.gz
./examples/hdtbl/color_transitions.ps.gz
./examples/hdtbl/mixed_pickles.ps.gz
./examples/hdtbl/short_reference.ps.gz
./examples/hdtbl/color_table_cells.ps.gz
./examples/hdtbl/color_nested_tables.ps.gz
./examples/hdtbl/color_boxes.ps.gz
./examples/hdtbl/chess_board.ps.gz
./examples/hdtbl/rainbow.ps.gz
./examples/mom/penguin.ps.gz
./examples/webpage.ps.gz
./examples/grnexmpl.ps.gz
./pic.ps.gz
./meintro.ps.gz
./meref.ps.gz
./meintro_fr.ps.gz
./ms.ps.gz