fixed TJ's bug in using main context instead of contextOrNil
changed behavior of checkClass method - empty server parameters will be turned to nil in the NSManagedObjective subclasses
added explanation comment and updated tests
Merge branch 'master' of github.com:MattFoley/CoreDataManager-iOS
Merge pull request #1 from seanwolter/master

updates to checkClass (including tests and comments in VIManagedObjectAdditions header)