Fix reverting unsaved changes for entities with custom (de)serialization
Merge pull request #56 from iosphere/pullrequest/revertUnsavedCustomDecode

Fix reverting unsaved changes for entities with custom (de)serialization
Added tests for NULL default-value handling
Fixed default values of NSNumber properties mapped to NULLable INTEGER/REAL fields
Added +databaseIsOpen and tests and checks for closed databases (fix #50)
Removed custom +tableName support, which was broken anyway (#57)
Kicking out NSCache with extreme prejudice. (It deadlocks easily in concurrent environments under memory pressure: http://openradar.appspot.com/10916098)
Merge remote-tracking branch 'marco/master'