rustc: Suppress derived pattern-match-checking errors

typeck::check::_match wasn't suppressing derived errors properly.
Fixed it.

src/test/compile-fail/issue-5100.rs

@@ -0,0 +1,44 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+enum A { B, C }
+
+fn main() {
+    match (true, false) {
+        B => (), //~ ERROR expected `(bool,bool)` but found an enum or structure pattern
+        _ => ()
+    }
+
+    match (true, false) {
+        (true, false, false) => () //~ ERROR mismatched types: expected `(bool,bool)` but found `(bool,bool,bool)` (expected a tuple with 2 elements but found one with 3 elements)
+    }
+
+    match (true, false) {
+        @(true, false) => () //~ ERROR mismatched types: expected `(bool,bool)` but found an @-box pattern
+    }
+
+    match (true, false) {
+        ~(true, false) => () //~ ERROR mismatched types: expected `(bool,bool)` but found a ~-box pattern
+    }
+
+    match (true, false) {
+        &(true, false) => () //~ ERROR mismatched types: expected `(bool,bool)` but found an &-pointer pattern
+    }
+
+
+    let v = [('a', 'b')   //~ ERROR expected function but found `(char,char)`
+             ('c', 'd'),
+             ('e', 'f')];
+
+    for v.each |&(x,y)| {} // should be OK
+
+    // Make sure none of the errors above were fatal
+    let x: char = true; //~ ERROR expected `char` but found `bool`
+}