BF: two bug fixes for ImageStim and new tests to prevent it in future

Might fix the problem with it not rendering on some gfx cards?

One was that the shader code was not correct - trying to use a 1D texture
instead of 2D. On my dev machine that caused the mask not to work but on
others might cause no image rendering at all?

The second was that the imagestim not being a lum image wasn't always
handled correctly (only apparent with a mask?)
DOCS: a few changes and added testimonials
Merge branch 'master' of github.com:psychopy/psychopy
DOCS: updated version number for new release

Conflicts:

	buildExeInstaller.nsi
	docs/source/changelog.rst
BF: fixed scaling issue with dotstim. Fixes #554

Since the refactoring this was applying the fieldSize variable twice. 
In the new scheme the base vertices should always only be -0.5<xy<0.5
and leave the scaling to field size to occur later.

Added a test to make sure that pos and field size respect units
in future (using a dense array of dots as a test image)
BF: MovieStim wasn't responding to setFlipVert() setFlipHoriz()

needed an update of the vertices after the method
Also added test to prevent regression