Patches to get number of tuples affected

Hi.
Here are some diffs that implement a function called TuplesAffected. It
returns the number of tuples the last command affected, or 0 if the last
command was a SELECT. I added it to the PgConnection because it contains
the Exec method as well as the PQresult structure. Maybe farther down in
the inheritance there should be a function that executes a query and
returns the number of tuples affected or returned (according to whether it
was a select or not) or a -1 on error.

Patches are attached...

-Michael