Send parameter types

[krlmlr]

libpq has an option to define the types of the parameters in PQprepare(). Can we make use of it? Does it allow getting rid of typecasting in DBItest?

[krlmlr]

Need to pass params to result_create() . Not infeasible, but postponing to get 1.4.0 out the door.

[krlmlr]

In a rewrite.