scour.py: Modify optimizeTransform to remove superfluous []s and ()s.

testscour.py: Add unit tests for Johan Sundström's fix for bug 722544, "SVG transform matrix() arg order is a1 b1 a2 b2 a3 b3, not a1 a2 a3 b1 b2 b3".

unittests/: Edit the unit tests' support files not to have a second line with the correct transformation. This is customarily in testscour.py.

unittests/transform-skewX-is-identity.svg

@@ -1,5 +1,4 @@
 <svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="0 0 9 9">
  <line stroke="rgba(255,0,0,0.5)" y1="9" x1="9" transform="skewX(0)"/>
- <line stroke="rgba(0,0,255,0.5)" y1="9" x1="9"/>
  <!--  skewX(0) is the identity transform, which can safely be removed -->
 </svg>