enhance pipe to support what we can do in hadoop streaming
add ut for pipe enhancement
update according to comments
update according to comments
Merge remote-tracking branch 'upstream1/master' into enhance_pipe
Merge remote branch 'upstream/master' into enhance_pipe
Merge branch 'enhance_pipe' of ssh://github.com/lyogavin/spark into enhance_pipe
refine comments and add sc.clean
Merge pull request #638 from lyogavin/enhance_pipe

Enhance pipe to support more features we can do in hadoop streaming