[Cairo] Preliminary PostScript output support in cairo-0.1.11

[Carl Worth]

I've just committed some proof-of-concept code for PostScript output
from cairo-0.1.11. (Have I mentioned yet that I have started posting
versioned tar files to http://cairographics.org/snapshots/ ? I guess I
have now.)

The essential new API functions are:

	void
	cairo_set_target_ps (cairo_t    *cr,
	                     FILE       *file,
	                     double     width_inches,
	                     double     height_inches,
	                     double     x_pixels_per_inch,
	                     double     y_pixels_per_inch);

	void
	cairo_show_page (cairo_t *cr);

There's a very simple demonstration program in cairo-demo/PS/basket.c
that demonstrates how easy it is to get matching PNG and PostScript
output. The PostScript output has multiple pages suitable for low-tech
flipbook animation. (Yes, this is proof that I shouldn't be writing
applications --- somebody, please put me out of the demo writing
business by writing better demos).

There are a few things to note about the current implementation (which
could definitely be improved on):

1) The output should have high-fidelity. Cairo doesn't depend on the
   PostScript interpreter to do anymore than display an image, and
   actually does all of its own drawing. This means that things like
   translucency still work even though PostScript doesn't support that
   directly.

2) As a side effect of (1), cairo has to compute rather large
   images. In order ease your pain, cairo uses zlib-based image
   compression in the PostScript output.

3) As a side effect of (2), current cairo-generated PostScript
   requires a LanguageLevel 3 PostScript interpreter. In my personal
   experience, I found that my laser printer does not like this input,
   but ghostscript is happy to accept it. (Also CUPS is even kind
   enough to provide an option to automatically down-convert to
   LanguageLevel 2 on the fly at printing time).

4) There really is just one big image per page in the output. There is
   no PostScript text, (nor any geometry), in the output at all. Yes,
   this is rather specious. Any help improving this will be gratefully
   accepted.

There are also a couple of other less important API functions that
have been added as part of this same work:

	void
	cairo_copy_page (cairo_t *cr);

	cairo_surface_t *
	cairo_ps_surface_create (FILE   *file,
		                 double width_inches,
			         double height_inches,
	                         double x_pixels_per_inch,
	                         double y_pixels_per_inch);

Have fun and Happy Printing!

-Carl