def load_backends():
<EOL>if not REPOSITORY_TYPES:<EOL><INDENT>for name in BUNDLED_BACKENDS:<EOL><INDENT>__import__('<STR_LIT>' % name)<EOL><DEDENT><DEDENT>return REPOSITORY_TYPES<EOL>
Load the backend modules bundled with `vcs-repo-mgr`.

:returns: The value of :data:`REPOSITORY_TYPES`.

When :data:`REPOSITORY_TYPES` is empty this function will import each of
the backend modules listed in :data:`BUNDLED_BACKENDS` before it accesses
:data:`REPOSITORY_TYPES`, to make sure that all of the :class:`Repository`
subclasses bundled with `vcs-repo-mgr` are registered.