Make various binops not typecheck for unsafe pointers. Closes #1173

Author: brson

src/comp/middle/ty.rs

@@ -2902,7 +2902,6 @@ fn is_binopable(cx: ctxt, ty: t, op: ast::binop) -> bool {
           ty_machine(ast::ty_f32.) { tycat_float }
           ty_machine(ast::ty_f64.) { tycat_float }
           ty_char. { tycat_int }
-          ty_ptr(_) { tycat_int }
           ty_str. { tycat_str }
           ty_vec(_) { tycat_vec }
           ty_rec(_) { tycat_struct }

src/test/compile-fail/binop-add-ptr.rs

@@ -0,0 +1,4 @@
+// error-pattern:binary operation + cannot be applied to type `*i`
+
+fn die() -> *int { (0 as *int) + (0 as *int) }
+fn main() { }