Cairo backend

[Fred Kiefer]

Some of you may have noticed that this week the release 1.0 of cairo has
been published. For quite some time GNUstep has had a backend based on
this graphics library. But this has always been incomplete and also
cairo has changed a lot over the months. In the last few weeks I cleaned
up the code for this backend and extended it a bit. Basically it is now
ready to try it, although many features are still missing.

Known limitations:
- fonts are still hard coded
- text in NSTextView sometimes doesn't get displayed
- images are often displayed incorrect
- copying from one GState to another uses wrong transformation
- some minor operations are missing or untested

I hope to solve these problems within the next month and will make a
public announcment for the cairo backend after that. If you find other
bugs, feel free to report them, or even better help to resolve them.

If you want to compile the cairo backend, use the command:

./configure --enable-graphics=cairo --disable-glitz

We probably should switch glitz off by default, as this is not offically
supported by cairo at the moment

Cheers
Fred