on LOAD DATA

Two problems :
1. LOAD DATA was not checking for SQL errors and was sending an OK
packet even when there were errors reported already. Fixed to check for
SQL errors in addition to the error conditions already detected.
2. There was an over-ambitious assert() on the server to check if the 
protocol is always followed by the client. This can cause crashes on 
debug servers by clients not completing the protocol exchange for some
reason (e.g. --send command in mysqltest). Fixed by keeping the assert
only on client side, since the server always completes the protocol 
exchange.