All overstayers flushed out by month's end, immigration corruption over - Big Joke     Thailand's super cop "Big Joke" has declared an end to corrupt practices at immigration offices and the deputy chief of police has said that the target for overstayers still in the kingdom by the end of November is "zero".   Deputy chief Gen Srivara Ransibrahmanakul and newly appointed immigration chief Maj-Gen Surachate "Big Joke" Hakparn were speaking to reporters after a meetin