BF: make integer division explicit for python 3
BF: make integer division explicit for python 3

Implicit integer division in finding colors in colormap.

alexis-roche/nipy,alexis-roche/register,nipy/nireg,bthirion/nipy,alexis-roche/nipy,alexis-roche/register,nipy/nireg,arokem/nipy,alexis-roche/nipy,nipy/nipy-labs,alexis-roche/nireg,alexis-roche/niseg,bthirion/nipy,bthirion/nipy,alexis-roche/nipy,bthirion/nipy,nipy/nipy-labs,arokem/nipy,alexis-roche/niseg,arokem/nipy,arokem/nipy,alexis-roche/nireg,alexis-roche/register