DEMO: mouse.py spot follows the mouse

(and reveals a current bug: fails to follow after one click)
Merge branch 'master' of git://github.com/psychopy/psychopy

* 'master' of git://github.com/psychopy/psychopy:
  BF: more agressive forcing of updates (fixes strange bug in setting of stim pos)
Merge pull request #494 from jeremygray/master

DEMO mouse.py dynamic position
BF: cumulative normal function

corrected small mistake in the function definition of the cumulative
normal and the inverse cumulative normal
ENH: comment cumulative normal function

added the new function definitions of the cumulative normal and its
inverse
Merge pull request #496 from PieterMoors/master

BF: correction to fit cumulative normal function
ENH: visual.Aperture now uses ShapeStim for its rendering - more flexible size and shapes can be used

Beforehand we could only create a radius and a fixed regular polygon (using
gluDisk) but now we can use arbitrary vertices and aspect ratios
Merge branch 'master' of git://github.com/psychopy/psychopy