#794 configurable $LIMITFLUSH and increase default value to 50000

[Che, Dong]

Hi Eldy:
I notice one way to inprove awstats on big log file stats(about 5 times fast than before with little memory usage increased) is setting $LIMITFLUSH to 50000(current default value is 5000). is it configurable or just increase the default value to 50000? because too small LIMITFLUSH caused a lot of temporay file I/O durring the update;

Thanks

Che Dong