PrimaryKeyConstraint objects (also UniqueConstraint not
completed yet). table creation and reflection modified
to be more oriented towards these new table-level objects.
reflection for sqlite/postgres/mysql supports composite
foreign keys; oracle/mssql/firebird not converted yet.
function in ANSICompiler
MySQLCompiler then skips most CAST calls since it only seems to support the standard syntax for Date
types; other types now a TODO for MySQL
then, polymorphic_union() function now CASTs null()s to the type corresponding to the columns in the UNION,
since postgres doesnt like mixing NULL with integer types
(long road for that .....)
Mike Bayer