MAHOUT-1615: drmFromHDFS returning the same Key for all Key,Vec Pairs for Text-Keyed SequenceFiles

SparkContext.sequenceFile(...) will yield the same key per partition for Text-Keyed Sequence files if the key a new copy of the key is not created when mapping to an RDD.  This patch checks for Text Keys and creates a copy of each Key if necessary.    
Can we please squirrel away lines 136-143 and all direct hadoop imports into a separate function, separate util helper object please? I am still very wary of direct hadoop dependencies and i predict this will not work on _all_ CDH /public hadoop releases.