Add new injection passes to makefile
Merge branch 'master' of github.com:halide/Halide
Made copy_to_dev do a dev_malloc if necessary
Merge branch 'master' of github.com:halide/Halide
Merge branch 'master' of github.com:halide/Halide
Large refactor of internal buffer_t handling.

create_buffer_t's now all made in one place, during storage flattening,
for every buffer. Useless ones get pruned later when removing dead lets.

copy_to_host, copy_to_dev, dev_malloc, dev_free, and setting dirty bits
pulled out of codegen_gpu_host and made into its own pass, so you can
see where they get injected

Added stubs for a new pass to inject syncthreads intrinsics. Not yet
implemented.

copy_to_dev now also does a dev_malloc if needed