Merge pull request #177 from birkenfeld/if_let_mini_fix

misc: fix check for unit body in "match -> if let" lint (fixes #172)

tests/compile-fail/match_if_let.rs

@@ -23,4 +23,16 @@ fn main(){
         (2...3, 7...9) => println!("{:?}", z),
         _ => {}
     }
+
+    // Not linted (pattern guards used)
+    match x {
+        Some(y) if y == 0 => println!("{:?}", y),
+        _ => ()
+    }
+
+    // Not linted (content in the else)
+    match z {
+        (2...3, 7...9) => println!("{:?}", z),
+        _ => println!("nope"),
+    }
 }