I've given up on trying to preserve the old code formatting
for compatibility. We're not planning on augmenting the algorithm
itself, just integrating it into cairo. So I don't expect to
make changes that we'll be all that interested in pushing
upstream.
The perceptualdiff program was written by Hector Yee with contributions
from Scott Corley and Mick Weiss. It is hosted at http://pdiff.sourceforge.net
The source code added here was obtained by:
svn co https://svn.sourceforge.net/svnroot/pdiff/trunk pdiff
which gave revision 22 of the source code.
The perceptualdiff program is available under the terms of the GNU GPL,
so I've added a note to COPYING about this program, (and the fact that
it is auxiliary only, and does not affect the license of the implementation
of cairo itself).
