Add deferred foreign keys DDL and DML.
Test showing Intersect_Ordered doesn't honor comparables
Handle nulls in MKeyComparables
Add the Persistit implementation.
Remove stray file.
Use TComparisons for comparing jump rows
Avoid null filled comparison list
Stale import
Don't generate tree names longer than the max supported.

Fixes #741
Test self-fk across differing types
Use KeyComparable for checking self-reference
Fix header
merge MMcM: Deferrable foreign key support

Merge pull request #1225 from MMcM/sql-layer/deferrable-foreign-key
https://github.com/FoundationDB/sql-layer/pull/1225
More SET CONSTRAINT cases
Should be else if
Make more ForeignKey protobuf fields optional for old databases.
merge nathanlws: Always use TComparisons in Intersect_Ordered

Merge pull request #1226 from nathanlws/sql-layer/fix-intersect-different-types
https://github.com/FoundationDB/sql-layer/pull/1226
merge nathanlws: Clamp tree name length to max supported

Merge pull request #1227 from nathanlws/sql-layer/clamp-tree-name-length
https://github.com/FoundationDB/sql-layer/pull/1227
merge nathanlws: Use KeyComparable for checking self-reference

Merge pull request #1228 from nathanlws/sql-layer/fk-self-reference-different-types
https://github.com/FoundationDB/sql-layer/pull/1228
merge nathanlws: Fix SET CONSTRAINTS ALL

Merge pull request #1229 from nathanlws/sql-layer/fix-set-constraint-all
https://github.com/FoundationDB/sql-layer/pull/1229