auto merge of #4747 : sanxiyn/rust/integral-type, r=graydon

`ty::type_is_integral` returns `true` for `ty_bool`. This causes `-true` to compile, instead of resulting in a type error.

src/test/compile-fail/unop-neg-bool.rs

@@ -0,0 +1,3 @@
+fn main() {
+    -true; //~ ERROR cannot apply unary operator `-` to type `bool`
+}