/**
* As this function relies on the InterBase API function isc_dsql_sql_info()
* which has a couple of limitations (which I hope will be fixed in future
* releases of Firebird), this function is fairly useless. I'm leaving it
* in place for people who can live with the limitations, which I only
* found out about after I had implemented it anyway.
*
* Currently, there's no way to determine how many rows can be fetched from
* a cursor. The only number that _can_ be determined is the number of rows
* that have already been pre-fetched by the client library.
* This implies the following:
* - num_rows() always returns zero before the first fetch;
* - num_rows() for SELECT ... FOR UPDATE is broken -> never returns a
* higher number than the number of records fetched so far (no pre-fetch);
* - the result of num_rows() for other statements is merely a lower bound
* on the number of records => calling ibase_num_rows() again after a couple
* of fetches will most likely return a new (higher) figure for large result
* sets.
*/