Improvements
------------
- Add whitespace around "<<", ">>", "+", "-", "*", "/", and "%" operators.
This helps to avoid confusion in tracers, since they run before parameter
substitution: for example, sqlparse parses "expr+%s" as "expr", "+%", "s"
rather than "expr", "+", "%s".
- Implement __getitem__ on bound ReferenceSets.
- The storm.twisted.testing.FakeTransactor test helper now uses a fake
transaction by default, so tests won't perform real commits as it's
not generally needed (bug #1009983).
- A new block_access context manager blocks database access for one
or more stores in the managed scope (bug #617182).
- Implement is_empty on bound ReferenceSets.
Bug fixes
---------
- Stop using deprecated assertEquals/assertNotEquals unittest methods.
- Return self from Empt...