bugfix for Join
test for Join
test revision
add test for And
and implementation
helper method added for logical plan modification, for external plan optimizer
bugfix for CollapsingAggregate
add distinct && countDistinct && tests
Merge pull request #13 from XingCloud/cleanup

Cleanup
add getAllsubscribers method and support setput null logical operator
first implementation on dag support
change exec/ref hadoop version
Merge pull request #15 from XingCloud/I8_dag_support

first implementation on dag support
sql utils work
Static logical plan