- move comparison of types, server default to the context.

- move comparison of types, server default to the context.
PG context in particular does some tricks to help these.
- But since type/default comparison is still loaded with surprises,
particularly the MySQL/MSSQL TINYINT/BIT-> boolean thing which we
can work around but haven't yet, turn both off by default.  They
aren't super useful compared to the huge number of wrong results
they can currently emit.
- Also add a plugin system for type/server default comparison.
- everything works but we're coding way ahead of tests at this
point