The format of the string data used in the imageop module is described

The format of the string data used in the imageop module is described
as "This is the same format as used by gl.lrectwrite() and the imgfile
module."  This implies a certain byte order in multi-byte pixel
formats.  However, the code was originally written on an SGI
(big-endian) and *uses* the fact that bytes are stored in a particular
order in ints.  This means that the code uses and produces different
byte order on little-endian systems.

This fix adds a module-level flag "backward_compatible" (default not
set, and if not set, behaves as if set to 1--i.e. backward compatible)
that can be used on a little-endian system to use the same byte order
as the SGI.  Using this flag it is then possible to prepare
SGI-compatible images on a little-endian system.

This patch is the result of a (small) discussion on python-dev and was
submitted to SourceForge as patch #874358.