tests/test-empty

mq: support "qimport --existing --name renametothis thatexistingpatch"

Before this change, the command would abort with a not too clear "patch
renametothis does not exist" error.

This change makes:
  qimport --existing --name renametothis thatexistingpatch
equivalent to:
  qimport --existing thatexistingpatch; qrename thatexistingpatch renametothis

#!/bin/sh

hg init a
cd a
hg log
hg grep wah
hg manifest
hg verify
ls .hg
ls .hg/store

cd ..
hg clone a b
cd b
hg verify
ls .hg
ls .hg/store