Implemented Histogram Intersection Kernel for histogram similarity

This way multiresHistogram() actually implements the Pyramid
Matching Kernel from Grauman&al.
For the current exp setup however it yields slightly worse results
than plain dot product. We'll see how it goes once spacial
awareness is back in: I'm aiming at the Spacial Pyramid Matching
from Lazebnik since it's important for me to discriminate mirror
images.
For real world control, spacial distinction is fundamental, and
pure histogram-based methods do not distinguish between mirror
images (or rotations, etc.). But a turn left expects a much
different control from a driver than a symmetrical turn right.

Let's see where we get.
Merge branch 'hotfix/0.5.1'