add regression test for set_inverse_instance on add_to_target
wrap logging around the actual query call itself.

This is to be consistent with the way the mysql2 adapter times queries
stop adding singleton methods to the PG connection
stop adding singleton methods to the mysql2 adapter
stop adding singleton methods to the SQLite3 connection
rm LogIntercepter
prepare the statement inside the begin / rescue block
log every sql statement, even when they error
log the statement name along with the SQL
instrumenter can't be cached because the app could be called from
different threads.