Blender Git Loki

Enable brush space attenuation for image painting as well as sculpting.
This makes it so that when using space with accumulate option, the
strength of the brush is attemuated to account for overlapping dabbing
of the brush. This way you don't get overblown areas while painting,
while still being able to paint over the same region repeatedly. To
enable this calculation, click on the lock icon next to the strength of
the brush when "accumulate" is selected.

This commit moves the attenuation factor calculation outside of sculpt
code and on stroke level. It also optimizes the curve integration to
only happen if the correct modes are enabled, while on sculpting it
occured always.