Conditionalized tests of bindvar emulation so they're not run for Oracle. Two of them don't work for Oracle (tries to do a "select" in db_exec_plsql) and since Oracle's definition of bindvar semantics defines the emulation semantics it seems silly to test if Oracle adheres to them or not :)
Added a simple caching mechanism to the database API as discussed (and approved) in TIP #57 many, many moons ago. Commands which are cache-enabled are db_string, db_0or1row, db_1row, db_list, db_list_of_lists, and db_multirow.