Fixing copy-paste bug in one of the group by optimization test. Big thanks to fujiy for catching this!
Adding static factory methods for creating ItemCollections.
As opposed to ctors these factory methods won't throw in case
of an error but will return all the errors as out collection
parameters. They will be used primarily by the EFDesigner.
Metadata unification: Removal of Code First SSDL serialization code path.

- Enables construction of StoreItemCollection from EdmModel.
- Fixes minor problems in Code First constructed store model.
- Enables SSDL validation from EDM validator.
- Adds required missing SSDL validation: EdmEntityContainer_DuplicateEntitySetTable.
- Further simplifies validation infra.
Codeplex workitem 655
Merge remote-tracking branch 'origin/master'