Add method to clear context from thread storage.
Fixed assert statement for abstract entities
Merge pull request #1 from magicalpanda/develop

Test Changes
It’s more desirable to ignore clang warnings for the individual lines where the dubious code occurs, rather than for a whole class.
Merge pull request #544 from BitSuites/develop

Update assertion of abstract entity types to use `isKindOfEntity:` rather than a pointer comparison
Merge pull request #542 from tonyarnold/feature/add-clear-context-method

Add method to clear the NSManagedObjectContext from thread storage for the current thread
Clears non-main thread cached NSManagedObjectContexts on cleanup. Fixes #335.