End slicing

Hi David,

I forgot to add single Int negative indexes for slicing. Here they are with tests.
DenseVector.scala line #63 and #68 had bugs too, I believe,  I changed " i > size " to " i >= size "

I forgot to check out when doing it, so some changes on the filtering branch are included too, sorry.

BTW, should I be worried about SliceMatrix.scala and SliceVector.scala as well? I couldn't quite figure out what they are doing...

Thanks,
Kenta