1.Introduce pgtype_attr_xxxx functions which take a typmod parameter as well as a...

1.Introduce pgtype_attr_xxxx functions which take a typmod parameter as well as a type oid parameter as an extension of pgtype_xxxx functions so that SQLColumns and SQLDescribeCol(SQLColAttrinute) could use common functions.
2.Call PQconnectdbParams instead of PQconnectdb when it's available.
3.Make cursor open check at transaction end a little more effective.
4.Added code for SQL_INTERVAL support and refcursor support though
  they are disabled.