Merge pull request #202 from dsharlet-intel/master

Fixing SPIR codegen for Intel CPU device
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.