Change behavior of cursor->rowcount and cursor->lastrowid

For compatibility with SQLAlchemy (close_with_result) values for lastrowid and rowcount should be retrieved immediately after execute/executemany, and stored in cursor->lastrowid and cursor->rowcount.

When using unbuffered result sets, rowcount should be updated per fetch.

Also the behaviour of rowcount and lastrowid should be changed:

rowcount:
In case of an error, or if statement wasn't executed rowcount should be -1 (see PEP-249)

• For DML statements the number of affected rows returned in OK packet by server:
  • > 0 for DML statements which modify or insert, e.g. ALTER TABLE or CREATE TABLE .. SELECT FROM
  • otherwise 0
• For DQL statement
  • if field_count > 0: number of rows returned
  • otherwise affected rows returned in OK packet by server.

lastrowid:

• if server returns no value (0) for last_insert_id, lastrowid should be None.
• if last_insert_id is > 0, return it's value