Consistent null adapter handling
Accessor for expressions
Lookup by table ID
Build an AIS-cached set of transforms for ALTER
Constraint checking goes through transform cache.
Index building goes through transform
OnlineHelper gets instantiated
Cleanup
Use proper constructor
merge nathanlws: OnlineHelper caches transformation info

Merge pull request #1074 from nathanlws/sql-layer/online-cached-transforms
https://github.com/FoundationDB/sql-layer/pull/1074
Minor issues in Hex and Unhex implementations.
Add TO_BASE64 and FROM_BASE64 functions.
Add YAML tests for them.
Update the Views table and the Parameters table with new column names.
Add two new columns to the parameters table. Fix resulting broken tests.
merge MMcM:  Add TO_BASE64 and FROM_BASE64 functions.

Merge pull request #1075 from MMcM/sql-layer/base64-funs
https://github.com/FoundationDB/sql-layer/pull/1075
Consistently pass Session along with StoreData.
Merge branch 'storage-description-session' into fdb-merge-fc107ff7
React to changes.
Make all (well, most) access to the database use a consistent Iterator pattern into the FDBStoreData.
Centralize how that iterator is built in anticipation of making it generic on the storage format.
merge MMcM: Consistently pass Session along with StoreData.

Merge pull request #1077 from MMcM/sql-layer/storage-description-session
https://github.com/FoundationDB/sql-layer/pull/1077