Fully support collations for clustered collections:

• creating a clustered collection with a collation
• performing bounded scans or lookups when the collection and query collations match

There's an initial attempt on this branch https://github.com/10gen/mongo/tree/dgomezferro/SERVER-61260-impl-collators (PR for context: https://github.com/10gen/mongo/pull/2557 ),that's probably missing integration with sharding.