Support for monochrome displays

[Martin Pool <mbp humbug org au>]

I have an old Sun ELC working as an XTerm.  GTK+-1.0.0 works quite
well on its monochrome screen, but I thought it would be nice to
improve support a little bit.  It's probably not the most important
thing in the world, but it would be good to keep up Linux's support of
older hardware.

After starting to read the code, it seemed like the thing to do would
be to initialize the style's GCs differently depending on the colour
depth.  The GC structure would also need a new field holding the
parameters to XSetDashes.

Specifically, I think GTK should probably use dashed lines and
stippled areas where it would normally use different colours.  For
example, drawing a raised rectangle on a 1-bit depth would look better
with the top & left edges drawn with a --*-- dash pattern, and the
bottom and right edges drawn solidly.  (Currently, the top and left
are drawn in white-on-white.)

    +  -  -  -  -  -  -  -+
     			  |
    |    Hello, World!	  |
			  |
    +---------------------+

I'd really appreciate comments from a GTK sensei.

--
Martin Pool

"How about the twelve foot tall Romanian giants wizards use for things
they wouldn't touch with a ten foot Pole?"      -- joez