Avoid flattening face-varying primvars during export.

[sirpalee]

Changes proposed in this pull request

• Importing face-varying primvars as indexed values.

Issues fixed in this pull request Fixes #6

Note: Thanks to @LumaPictures who already had this fixed in their USD fork!

[JamesPedFoundry]

Hi Pal, Apologies for the delay in getting back to this, I've done some testing across a few other renderers and Primvars and it looks good to go. Would you mind sending me your contact details (email will do), such that I can send over a CLA such that we can accept this pull request :)? The CLA is something we require to be signed to accept changes into our public repository, similar to the Pixar USD repository this stemmed from.

You can send them to james.pedlingham@foundry.com, thanks, and thanks again for providing this patch! James