This fixes a problem with GDK and colour conversion across big/little
endian displays: GDK has a slight problem when displaying on 15bpp
visuals across machines of different endianness (e.g. try a little-endian
X server with 5 bits per colour, r/g/b masks 0x7c00/0x3e0/0x1f, run
gimp from a big-endian machine displaying onto that X server [or vice
versa] -> the colours are pretty much messed up). This patch fixes the
problem (missed out the most significant bit of green when converting).

Martin Maierhofer <martin.maierhofer@eu.citrix.com>