Optimised Object::memoryUsage()

- Reduced number of set lookups by performing find/insert in one
- Removed bookkeeping for objects with only one owner - they should never be counted twice anyway

This knocks 20% off the total runtime of a certain Gaffer benchmark.
Added support for uniform arrays in GLSL shaders
Merge pull request #361 from danieldresser/uniformArrays

Added support for uniform arrays in GLSL shaders
Update Changes for 9.0.0-a11
Update SConstruct for 9.0.0-a11
Merge pull request #359 from johnhaddon/memoryAccumulatorOptimisation

Optimised Object::memoryUsage()
David has no objections, and Andrew isn't here today to object, going ahead and pulling this one.
Updated Changes ( merged one more pull request before releasing 9.0.0-a11 )
Added ToGLSphereConverter.

This is necessary to be able to see primitive spheres in Gaffer, because the new GL scene graph code relies entirely on CachedConverter for conversions.
Merge pull request #362 from johnhaddon/toGLSphereConverter

Added ToGLSphereConverter.