Refresh destination object when an insert fails, prevent dangling relationships.
Don't try to insert a nil object to the array.
Merge pull request #223 from baarde/skip_fault_relationships_update

Skip relationships that are fault when updating backing object with managed object
Merge pull request #221 from Spaceman-Labs/bugs/dangling_relationship

Prevent dangling relationships when an insert save fails
Minor refactoring
Merge pull request #220 from Spaceman-Labs/bugs/notifications

Fix reversed context notifications
[Issue #217] Using backing object ID cache
Merge branch 'master' of https://github.com/AFNetworking/AFIncrementalStore
Merge branch 'master' into serenity_store
Merge branch 'develop' into serenity_store
Merge branch 'serenity_store' of https://github.com/cshumway/AFIncrementalStore into serenity_store