Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' of https://github.com/halide/Halide
Fix compilation error on os x
Fixed timing code for sort.
Added fusion-in-tiles to lesson 8
Slop test was too strict for 32-bit builds.
Avoid dependence on llvm's internal Config.h

(We were using it to get the llvm version)
Merge branch 'master' of https://github.com/halide/Halide
Fixed multiple contexts being created/shared incorrectly.
Removed DEBUG_PRINTF macro
Fixed attempt to reuse freed OpenCL platform
Merge pull request #197 from dsharlet-intel/master

Using a single global context for OpenCL
Added math function definitions to OpenCL C codegen
Merge branch 'master' of https://github.com/halide/Halide
Added a tutorial on reductions.

Also updated tutorial todos.
Text changes in latest tutorial.