TAJO-498: Implement digest(text, text) function. (DaeMyung Kang via hyunsik)
TAJO-522: OutOfMemoryError: unable to create new native thread. (hyoungjunkim via hyunsik)
TAJO-531: Fix warnings in tajo-client. (jinho)
TAJO-535: Fix warnings in tajo-rpc. (jinho)