renamed ARCH32 and ARCH64 to APPLESEED_ARCH32 and APPLESEED_ARCH64.
Merge pull request #479 from sriravic/curve_upstream_PR

Curve Rendering PR Commit - Basic Curve Loading - Curve Tree - Rendering...
Merge branch 'master' of github.com:appleseedhq/appleseed
fixed comment and minor cosmetic tweaks.
added a comment.
Fixed some minor issues