When pulling from a non hg repository URL (e.g. http://www.kernel.org/hg) you geta pretty obscure error (zlib: uknown compression type). The attached patch modifies hgweb.py and hg.py to supply and check a 'Content-type: application/hg-0.1' HTTP header for the branches, between and changegroup commands, so that we know it's a proper hg repo before snarfing the input. Comments appreciated!

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "0 0"

echo 123 > b
hg add b
hg diff | sed "s/\(\(---\|+++\).*\)\t.*/\1/"

hg diff -r tip | sed "s/\(\(---\|+++\).*\)\t.*/\1/"