Fixed shortest-path kernel bug and adjusted results to MATLAB impl.

FIX: Rogue pointer when reading graph-specific label files.
ENH: Made ShortestPathKernel results conform to (original) MATLAB impl
     of Nino Shervashidze (see, JMLR article on WL kernel)
STYLE: Some TubeTK style adjustments.
Change-Id: Iaec77ebcb812955c635303b09213f41705a9bd11
Added test for Shortest-Path kernel + MIDAS key file.

Change-Id: I6a0f7b86a6817354d2382781730c97a2101f0d60
Merge topic 'rk-GraphTests'

76f6479 Added test for Shortest-Path kernel + MIDAS key file.
7dae4cd Fixed shortest-path kernel bug and adjusted results to MATLAB impl.