QPID-6150: Add __init__.py to setup.py for linear store.

The file was not being included in the source tarball.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1631819 13f79535-47bb-0310-9956-ffa450edef68
NO-JIRA: Change python.i to qpid_messaging.i in extra build
QPID-6170: Adds build support for aarch64 and ppc64le architectures.

Contributed by Marcin Juszkiewicz <mjuszkiewicz@redhat.com>