[cairo] libpixman API renames completed

[Carl Worth]

On Dec 10, Dave Beckett wrote:
 > I've completed the next stage of merging libpixregion and libic,
 > renaming the functions, types, enums to have a prefix of pixman or
 > PIXMAN (enum values).

Many thanks Dave!

 > That finishes my work on the libpixman merge.  There are of course,
 > other cleanups and fixes now possible - so, go ahead!
 > 
 > Of course now cairo itself can be changed to use it.

Done, (also thanks to Dave).

So, cairo has gone from four modules (slim, libpixregion, libic, and
cairo), down to only two: libpixman and cairo.

-Carl