disable MSAA for the picking

MSAA can and will result in mixed colors which is a problem if we use
the color for the selection.

Change-Id: Ifbd6d37902069b26e714d2e3e5576fb767f9fbbf
use a step width of 10 for the picking color

Change-Id: Icdf7653e9dc5a33d78381b9ea5f3fd4652b1be5a
Revert "loplugin:unreffun"

This reverts commit 7686f93f58ae3eed7ed2ee2bead362d034e24c02.
enable picking again

Right now with an ugly work-around. The image is vertically flipped so
we just adapt our access to it.

Change-Id: I0128f54d4a0fbe697dc8726f6e255111ecb8412f