Makefile.am: Tweak terse-output formatting
Rework camera field-of-view setting

In particular, keep track of which axis was last used to set the FOV,
which will be the one we preserve when changing aspect ratio.
load-pbrt.lua: Get rid of kludge when changing image dimensions

... now that the camera preserves the field-of-view which was last set,
even when the aspect-ratio changes, we don't need to worry about it.