Multilink fixes and optimizations: - Optimisation: Late evaluation of Multilinks (only in rdbms backends): previously we materialized each multilink in a Node -- this creates an SQL query for each multilink (e.g. 'files' and 'messages' for each line in the issue index display) -- even if the multilinks aren't displayed. Now we compute multilinks only if they're accessed (and keep them cached). - Add a filter_iter similar to the existing filter call. This feature is considered experimental. This is currently not used in the web-interface but passes all tests for the filter call except sorting by Multilinks (which isn't supported by SQL and isn't a sane concept anyway). When using filter_iter instead of filter this saves a *lot* of SQL queries: Filter returns only the IDs of Nodes in the database, the additional content of a Node has to be fetched in a separate SQL call. The new filter_iter also returns the IDs of Nodes (one by one, it's an iterator) but pre-seeds the cache with the content of the Node. The information needed for seeding the cache is retrieved in the same SQL query as the ids.

class MockNull:
    def __init__(self, **kwargs):
        for key, value in kwargs.items():
            self.__dict__[key] = value

    def __call__(self, *args, **kwargs): return MockNull()
    def __getattr__(self, name):
        # This allows assignments which assume all intermediate steps are Null
        # objects if they don't exist yet.
        #
        # For example (with just 'client' defined):
        #
        # client.db.config.TRACKER_WEB = 'BASE/'
        self.__dict__[name] = MockNull()
        return getattr(self, name)

    def __getitem__(self, key): return self
    def __nonzero__(self): return 0
    def __str__(self): return ''
    def __repr__(self): return '<MockNull 0x%x>'%id(self)
    def gettext(self, str): return str
    _ = gettext