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

Conflicts:
	Makefile
Cleaned up target feature enumeration and corresponding string mapping.
Updated for target feature enumeration changes.
Fixed tabs vs. spaces.
Windows build tweaks
Merge branch 'master' of https://github.com/halide/Halide
Further windows build fixes. Now builds against pnacl llvm too.
Fix -pedantic error
Add noduplicate in Target.cpp instead of ptx_dev.ll

noduplicate doesn't exist in release-3.2
Only test gpu targets with trunk

Because llvm 3.4 and earlier duplicate syncthreads incorrectly
and you get race conditions.
Allow parallel rvars with a warning
Merge branch 'master' into compute_cached

Conflicts:
	Makefile
	src/Lower.cpp
	src/Schedule.h
Missed in merge.
Couple more merge issues.
Suppress warning about parallelizing rvars when we can prove it's safe.
Allow reordering "pure" rvars.
Made the bad rvar reorder example actually bad.

Before it was technically OK.
Add code to give better error message when using an undefined RDom dimension.
(Fixes https://github.com/halide/Halide/issues/332 )

Add test for above.

Remove use of double underscores in identifer as these are reserved in C++.
If a buffer is not written to and is accessed uniformly w.r.t. thread indices, put it in constant memory.
Fixed OpenCL double support.