Give at least one of the allowed arities instead of -1.
Consolidate, standardize and extend the CURRVAL & NEXTVAL functions.
More YAML tests.
Correct error message.
merge MMcM:  Consolidate, standardize and extend the CURRVAL & NEXTVAL functions.

Merge pull request #1082 from MMcM/sql-layer/currval-one-arg
https://github.com/FoundationDB/sql-layer/pull/1082
Squashed