Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' of https://github.com/halide/Halide
Added undef intrinsic.

Stores that would store an undef are skipped. This lets you write in-place
updates to an output buffer and functions with update steps and no pure steps.

See the two new tests (undef and in_place) for example usage.
Fix for loading grayscale pngs using Halide's Image class (not static_image)
Merge branch 'master' of github.com:halide/Halide
Fix PTX math test failure.
Remove redundant include.
Merge branch 'master' of https://github.com/halide/Halide
Removed shared_ptr dependency from static_image
Merge branch 'master' of github.com:halide/Halide

Conflicts:
	apps/support/static_image.h
Added linking to libcuda to the static tests
Only link static tests to libcuda if WITH_PTX defined
Only compile static tests for ptx if HL_TARGET includes ptx or cuda
Third time's the charm (only link tests to cuda when HL_TARGET includes CUDA)
Don't test ptx with llvm 3.2
Merge branch 'master' of https://github.com/halide/Halide
Added a new scheduling tutorial on two-stage pipelines.

Also minor corrections to other lessons.
Merge branch 'master' of https://github.com/halide/Halide
Add some missing cases to IREquality
Merge branch 'master' of https://github.com/halide/Halide