Image scaling routine with correct gamma handling

There is a widespread problem with [gamma error in picture scaling](http://www.4p8.com/eric.brasseur/gamma.html). It would be nice to have a version of `image.scale` with proper gamma handling, for use in the relevant circumstances.

Migrated-From: http://trac.imagej.net/ticket/38

Start by locating the image.scale routine and reviewing how it handles pixel values during scaling. Use the linked gamma-handling reference to define the relevant circumstances and expected behavior; done means a gamma-correct scaling variant is available for those cases.

Written by the indexing model from the issue text.