This tells big endian systems that the data is in ABGR instead of RGBA.
It should be ignored on little endian systems!
Add support in Amiga platform code.
-> All platform code that could be compiled for big endian systems will need
to be updated to recognise BITMAP_ABGR. This includes GTK and
Framebuffer frontends. Both BITMAP_ABGR *and* the endianness of the host
will most likely need to be checked and the allocated bitmap format
and/or bitmap plotter changed to handle ABGR component order.
svn path=/trunk/netsurf/; revision=9108
