Stop interpreting SQL 'string' columns as :string type.

SQL doesn't have a string type, and interpreting 'string' as text is
contrary to at least SQLite3's behavior:

"Note that a declared type of 'STRING' has an affinity of NUMERIC, not TEXT."
http://www.sqlite.org/datatype3.html
Merge pull request #11922 from Empact/string-confusion

Stop interpreting SQL 'string' columns as :string type.