Add groupby support on dataframes to SparkLing pandas. Add a helper method to make a distributed dataframe from a local dataframe (this results in types being reguessed so it is less than ideal), add back in a run-tests script that can yell if SPARK_HOME isn't set (whereas directly using nose just resulted in no output). Add inital code coverage, although we might want to disable it since it only reports on things which run locally and most of our stuff runs remotetly. Remove some dead code from utils. Also update unittest library to unittest2.