[cairo] CAIRO_DEBUG, take 2

[Chris Wilson]

Although there's still a bit more to incorporate from Behdad's feedback,
I'd like people to have a look over the cairo-debug branch. It's
hopefully now at a level of basic functionality that should encourage
everyone to use and improve it...

The code can found at git://people.freedesktop.org/~ickle/cairo under
the branch cairo-debug.

In terms of debugging API, it offers:
	_cairo_debug_maybe_printf(),
	_cairo_debug_maybe_backtrace_or_abort()
which check for an enabling flag in CAIRO_DEBUG, along with more
low-level functions:
	_cairo_debug_printf(),
	_cairo_debug_backtrace()
	etc.

So far, through CAIRO_DEBUG, you can generate uncompressed pdf output,
force the use of fallback images and fonts in the pdf/ps/svg backends
and trigger a backtrace on a cairo_error(). (The backtrace now tries to
use the better backtrace_symbols() from utils/backtrace-symbols.c.)

Thanks.
-- 
Chris Wilson