Fix the error-patterns in 2 cfail tests. Issue #855

src/test/compile-fail/binop-bitxor-str.rs

@@ -1,3 +1,3 @@
-// error-pattern:^ cannot be applied to type `str`
+// error-pattern:^ cannot be applied to type `istr`
 
 fn main() { let x = "a" ^ "b"; }

src/test/compile-fail/minus-string.rs

@@ -1,3 +1,3 @@
-// error-pattern:applying unary minus to non-numeric type str
+// error-pattern:applying unary minus to non-numeric type istr
 
 fn main() { -"foo"; }