Improved vectorize test by promising width == vector size
Improved vectorize test by promising width == vector size

Otherwise the new bounds clamping mechanism triggers and slows things down
very slightly.


Former-commit-id: 8ea8df545d49e370b073aec9715bc7b80b3c62df
Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide