Throw exception if the parameter `y` in the expression `x in y` contains None value(s)
Fixes #19: Workaround for Python 2.6 string exceptions bug
Small change in SQL UPDATE command: add spaces around '=' in SET column = value
Status renamed: locked -> to_be_checked
Entity._construct_optimistic_criteria_() method refactored out of Entity._save_updated_()
Add optimistic checks to Entity._save_deleted_()
Using of optimistic checks in non-optimistic mode
SQLTranslator JOIN bug fixed
Refactoring of QuerySetMonad
Merge 'master' into 'orm'