[cairo] OS/2 backend support files

[Doodle]

Hi all,

Following my conversation with Carl in public, here is a zip
file containing the OS/2 specific files for Cairo v1.2.0.

http://scenergy.dfmk.hu/doodle/cairo_120_os2_files.zip

This contains the OS/2 surface support files, and some small
modifications in the common header files.

Please note that it does not contain the patches to the
build system, because I use OpenWatcom to build Cairo on
OS/2, so I have a completely different build system,
however, the OS/2 Mozilla guys are pushing me hard to
submit these files to the official distribution, so here
they are. (There is a promise from one of them that once
it gets in there, he'll create and submit the patches for
the build system.)

For your information, the zip contains 8 files, from
which 5 are completely OS/2 specific and does not interfere
with any of the current Cairo code (OS/2 surface support,
OS/2 DLL support, and so on...). Then there is a modified
cairo.h in there (cairo_surface_type_t extended with
CAIRO_SURFACE_TYPE_OS2), and there is a modified cairoint.h
(mutex declares for OS/2). The cairo-features.h is only there
for completeness, as that one is also needed on my side to
compile Cairo.

So, I'd like to ask to check out this zip and if it seems to be
ok, then include these files in the official Cairo distribution.

Thanks in advance!
   Doodle