When specifying the 'file' key to a value of it's own name, test
that this works and does not cause a false positive circular reference
error.
Signed-off-by: Mazz Mosley <mazz@houseofmnowster.com>
If the 'file' key is not set in the extends_options dict then we
look for the 'service' from within the same file.
Fixes this issue: https://github.com/docker/compose/issues/1237
Signed-off-by: Mazz Mosley <mazz@houseofmnowster.com>
