turning ri:automaticInstancing on by default
TIFFImageReader now checks if the tif is tagged as coming from tdlmake, and if so, sets the sourceColorSpace from the image description set by tdlmake.
Merge pull request #348 from davidsminor/autoInstancingDefaultOn

turning ri:automaticInstancing on by default
Reformatted for style consistency
Merge pull request #352 from danieldresser/linearizeTDLs

TIFFImageReader now checks if the tif is tagged as coming from tdlmake, ...
Merge remote-tracking branch 'upstream/master' into IECoreAppleseed
More work
Simplified AttributeState related code.