record: removed 'has_key' usage
Py3k has removed the dictionary has_key method. This patch implements
a one argument function that can be used as a callback by hg.revert in
the record extension.
#!/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