OpenCL runtime uses device index HL_GPU_DEVICE, renamed HL_OCL_PLATFORM -> HL_OCL_PLATFORM_NAME, HL_OCL_DEVICE -> HL_OCL_DEVICE_TYPE.
Merge pull request #352 from halide/opencl_gpu_device

OpenCL runtime uses device specified by HL_GPU_DEVICE
Fix warning.
Remove opengl from nightly tests, because it requires an active X11 display
Update gitignore
Add tutorial that demonstrates aot compilation
Add some intermediates to gitignore
Avoid redundant re-run of tutorial generators

They're already called by the corresponding runner
Merge branch 'master' of github.com:halide/Halide
More correct version of previous commit.
Add static test libs to static tutorials
Fix bug in RenameFreeVars mutator
Rework simplification of EQ to avoid an infinite loop.
Merge remote-tracking branch 'upstream/master'
Added erf function