Better error messages for div_round_to_zero and mod_round_to_zero.
Better error messages for div_round_to_zero and mod_round_to_zero.


Former-commit-id: fcd6ef55e9eb67048aa579e3089ec064ac98c6c5
darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide