Updates for llvm trunk changes
Constant integer division revamp
Merge branch 'master' of github.com:halide/Halide

Conflicts:
	cpp/src/CodeGen_ARM.cpp
	cpp/src/CodeGen_Posix.cpp
	cpp/src/CodeGen_X86.cpp
Added an exhaustive test for constant integer division tricks
Integrated Len Hamey's better definitions of signed div and mod
Added timing to the const_division test

Helps verify that the speed optimizations actually help
Re-enabled fast const division path for 8 and 32 bit on x86
Merge remote-tracking branch 'upstream/master'