Add tests for partition with string keys
Add two tests one with a string array and one from a textFile to test
both codepaths
Merge branch 'master' of github.com:amplab/SparkR-pkg into string-tests

Conflicts:
	pkg/inst/tests/test_textFile.R
Fix bug where serialized was not changed for RRRD
Reason: When an RRDD is created in getJRDD we have converted any
possibly unserialized RDD to a serialized RDD.
Merge pull request #30 from shivaram/string-tests

Add tests for partitioning with string keys