auto merge of #6669 : yjh0502/rust/fix_6209, r=graydon

Fix issue #6209, and some related issues about constant expression
 - unmatched type between arms
 - unmatched type in range

src/test/compile-fail/match-ill-type1.rs

@@ -0,0 +1,6 @@
+fn main() {
+    match 1 {
+        1..2u => 1, //~ ERROR mismatched types in range
+        _ => 2,
+    };
+}

src/test/compile-fail/match-ill-type2.rs

@@ -0,0 +1,7 @@
+fn main() {
+    match 1 {
+        1 => 1, //~ ERROR mismatched types between arms
+        2u => 1,
+        _ => 2,
+    };
+}