Add some comments clarifying isAccessible contract wrt not authenticated.
Change check for legal part of CREATE TABLE AS SELECT ... WITH DATA plan from disallowed to allowed.
Make the other comment clearer, too.
merge MMcM: Add some comments clarifying isAccessible contract wrt not authenticated

Merge pull request #1494 from MMcM/sql-layer/security-service-not-authenticated-comments
https://github.com/FoundationDB/sql-layer/pull/1494
merge MMcM: Change check for legal part of CREATE TABLE AS SELECT ... WITH DATA plan

Merge pull request #1495 from MMcM/sql-layer/create-table-as-select-is-illegal-plan
https://github.com/FoundationDB/sql-layer/pull/1495