if my pig script STOREs a relation, the order of rows in the relation is
normally not important.
but when I use pigUnit to test, the actual test on the STORE'ed variable is
a simple string comparison (or string array comparison).
so most of the times, the order of rows in the relation store'd into the
var is different from my desired order specified in the expected
looks pigUnit has to implement comparison really on relation, not on arrays