tests/test-clone

This fixes a bug that Chris Mason found.  As for a test case, I can't
think of one.  It's a very weird case.  Basically, if there is a file
listed as changed in the changelog entry, but not showing up in any
of the associated manifest entries, hg would abort when trying to
create a changeset.  Now it just decides the file must not have any
versions relevant to the changeset.

#!/bin/sh

mkdir a
cd a
hg init
echo a > a
hg add a
hg commit -m test -d '0 0'

# Default operation
hg clone . ../b
cd ../b
cat a
hg verify

# No update
hg clone -U . ../c
cd ../c
cat a
hg verify

# Default destination
mkdir ../d
cd ../d
hg clone ../a
cd a
hg cat a