Added an iscolor flag to io.cpp method ReadImageToDatum to handle grayscale images and a corresponding commandline flag [-g] to convert_imageset.cpp.
Changed variable name: iscolor to is_color.
pycaffe: leave grayscale images gray according to arg
Merge pull request #469 from weinman/grayscale-io-convert

Add grayscale input processing for intensity images in tools and
pycaffe.