Add cuda compute capabilities 3.0, 3.5, 5.0

Untested.
Fix readme typo
Merge branch 'master' of github.com:halide/Halide
Target::has_gpu_feature() should return true for OpenGL
cherry-pick some cleanups from pull request #370
Merge branch 'master' of github.com:halide/Halide
Clarify why has_gpu_feature doesn't count OpenGL
Add ability to programmatically set HL_TRACE_FILE
Add ability to set number of threads programmatically.
Fixed uninitialized constant_bytes, fixes #368.
Make it possible to set the gpu device selection vars programmatically
Add missing file to last commit.
Be slightly less clever about gpu_device = -1
opengl.cpp: create_kernel() should log shader src a line at a time

Android logcat implementations often limit output to ~1000 char chunks
at a time; log the shader a line at a time to avoid it being clipped.
(DEBUG-only.)
Update in response to discussion. Still untested and unsuitable for merge.
Document lifetime for char * args and return values in HalideRuntime
Add some more comments to HalideRuntime.h
Merge pull request #376 from halide/gpu_device_selection

Gpu device selection
Upgrade python bindings to Halide release_2014_07_16
Merge pull request #378 from fcr/master

Upgrade python bindings to Halide release_2014_07_16