command line templates: add formatnode filter
This will print a full hash node with --debug and a short one otherwise.
Use it with some default templates and in map-cmdline.default to print
the parents. This should fix issue538.
#!/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
hg diff -r ""
hg diff -r tip -r ""
true