Improve bounds calculation for divide-by-constant

Apply similar optimizations to those already found in
multiply-by-constant.
Merge pull request #200 from steven-johnson/master

Improve bounds calculation for divide-by-constant
Cleanup cpuid function.
Merge pull request #201 from florian-kriener/cpuid_cleanup

Cleanup cpuid function.
A restricted version of fast division logic for runtime divisors.

Turns out the most complex method works for all divisors (except for 1).

Seems to be a win when there's a multiply-keep-high-half
instruction available. We could make this the default implementation
of division, but it's restricted to small divisors and is slower for
32-bit numerators on my machine. Run test/performance/const_division.cpp
for performance numbers on your machine.
Merge branch 'master' of github.com:halide/Halide
Fixed address space metadata per current SPIR spec
Merge branch 'master' of https://github.com/halide/Halide
Merge pull request #202 from dsharlet-intel/master

Fixing SPIR codegen for Intel CPU device
Add support for passing a void * user context value to Halide functions; if present,
this pointer is passed through to Halide runtime routines (halide_malloc, halide_printf,
etc.)

This change requires that all existing user-written Halide runtime routines be modified
to take a void * parameter as their first argument.
Address pull request comments.

Renamed get_user_context() in Param.h to user_context_param(), so as to not
clash with CodeGen::get_user_context().

Added user_context as an explicit argument to halide_assert in HalideRuntime.h.

Various indentation and formatting fixes.
Added dummy kernel to avoid empty program errors on some OpenCL implementations
Merge branch 'master' of https://github.com/halide/Halide
Avoids loss of low significant bits in conversion from float to string
Turned on FP_CONTRACT for OpenCL programs.
Fixed least significant bits of floats causing errors for C targets.
Fixed precision upper bound
Changed from L to ULL suffix on integer constants in the division tables
update to call_count was getting elided if we don't read from it
Added spir_common_dev.ll with most math functions implemented