Anti-aliased renderer

[Alexander Larsson]

I've started work on an anti-aliased libart_lgpl based renderer for dia.
I've checked in my current code in cvs. Use view->AntiAlias to toggle
between the gdk and aa renderer. 

The aa renderer doesn't support all functions yet. It doesn't do beziers,
images or text. The draw_pixmap_line (used by eg. grid) also doesn't
support dashes.

/ Alex