contrib: add Chris Mason's stand-alone diff tool
This uses Mercurial's diff algorithm to generate unidiffs like the traditional diff tool.
#!/bin/sh
#
mkdir t
cd t
hg init
echo 0 > a
echo 0 > b
hg ci -A -m m -d "0 0"
touch nottracked
hg locate a
hg locate NONEXISTENT
hg locate
hg rm a
hg ci -m m -d "0 0"
hg locate a
hg locate NONEXISTENT
hg locate
hg locate -r 0 a
hg locate -r 0 NONEXISTENT
hg locate -r 0