Prepare for Pig 0.8.1 release

[Daniel Dai]

Hi, Pig developer
Since Pig 0.8.0 release, we have fixed quite a few bugs. Now it is a 
good time to plan another Pig 0.8 release. We hope to push the release 
in one to two weeks. We still have a couple of bugs planning to fix 
(PIG-1892, maybe PIG-1912, PIG-1895, PIG-1814, PIG-1826) before release. 
Besides that, does anybody has some patches wants to get in?

Thanks
Daniel