Merge pull request halide#496 from halide/ramp_div_mod_simplify_rules

Rework and add new rules for simplifying ramp/x and ramp%x

Merge pull request halide#376 from halide/gpu_device_selection

Gpu device selection

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

Merge pull request halide#282 from white-pony/master

Added minval_f32/maxval_f32 functions for the OpenCL target

Fix bug in simplify that was skipping saturating arm ops

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

Fixes to old windows build method.

Merge pull request halide#179 from jansel/master

Print warnings to stderr instead of stdout

Merge branch 'master' of github.com:halide/Halide