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
# test dirstate._dirs refcounting
hg init t
cd t
mkdir -p a/b/c/d
touch a/b/c/d/x
touch a/b/c/d/y
touch a/b/c/d/z
hg ci -Am m
hg mv a z