tests/test-diffdir

Add -D/--nodates options to hg diff/export that removes dates from diff headers
and replace uses of sed in the tests with --nodates.

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "1000000 0"

echo 123 > b
hg add b
hg diff --nodates

hg diff --nodates -r tip

echo foo > a
hg diff --nodates