Log Message:
1.5.3:

* enum34 dependency is forced to be at least version 1.1.3. Fixes spurious
bug related to enum classes being falsy in boolean context, which caused
_Inconsistent Hierarchy_ `RuntimeError` in `singledispatch` module.

* Do not raise an exception when uninferable value is unpacked in ``with`` statement.

* Lock objects from ``threading`` module are now correctly recognised
  as context managers.