MAHOUT-1500: ValueString API changes

Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1500: Simplify empty_frame()

Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1500: Use ArrayUtils.add() wherever possible

Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1500: Style fixes

Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1500: Detect seqfile format

If not sequence file (first three bytes == 'S', 'E', 'Q') then
fallback to H2O parallel/efficient parser of CSV and other formats

Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1500: Use int key as row number into matrix in parser

Signed-off-by: Anand Avati <avati@redhat.com>
MAHOUT-1500: Do away with scala.Tuple2 usage

Signed-off-by: Anand Avati <avati@redhat.com>