Fix FP with mut_mut and for loops

tests/compile-fail/mut_mut.rs

@@ -2,16 +2,15 @@
 #![plugin(clippy)]
 
 #![allow(unused, no_effect, unnecessary_operation)]
+#![deny(mut_mut)]
 
 //#![plugin(regex_macros)]
 //extern crate regex;
 
-#[deny(mut_mut)]
 fn fun(x : &mut &mut u32) -> bool { //~ERROR generally you want to avoid `&mut &mut
     **x > 0
 }
 
-#[deny(mut_mut)]
 fn less_fun(x : *mut *mut u32) {
   let y = x;
 }
@@ -21,7 +20,6 @@ macro_rules! mut_ptr {
     //~^ ERROR generally you want to avoid `&mut &mut
 }
 
-#[deny(mut_mut)]
 #[allow(unused_mut, unused_variables)]
 fn main() {
     let mut x = &mut &mut 1u32; //~ERROR generally you want to avoid `&mut &mut
@@ -29,15 +27,38 @@ fn main() {
         let mut y = &mut x; //~ERROR this expression mutably borrows a mutable reference
     }
 
+    if fun(x) {
+        let y : &mut &mut u32 = &mut &mut 2;
+        //~^ ERROR generally you want to avoid `&mut &mut
+        //~| ERROR generally you want to avoid `&mut &mut
+        //~| ERROR generally you want to avoid `&mut &mut
+        **y + **x;
+    }
+
     if fun(x) {
         let y : &mut &mut &mut u32 = &mut &mut &mut 2;
         //~^ ERROR generally you want to avoid `&mut &mut
         //~| ERROR generally you want to avoid `&mut &mut
         //~| ERROR generally you want to avoid `&mut &mut
         //~| ERROR generally you want to avoid `&mut &mut
+        //~| ERROR generally you want to avoid `&mut &mut
+        //~| ERROR generally you want to avoid `&mut &mut
         ***y + **x;
     }
 
     let mut z = mut_ptr!(&mut 3u32);
     //~^ NOTE in this expansion of mut_ptr!
 }
+
+fn issue939() {
+    let array = [5, 6, 7, 8, 9];
+    let mut args = array.iter().skip(2);
+    for &arg in &mut args {
+        println!("{}", arg);
+    }
+
+    let args = &mut args;
+    for arg in args {
+        println!(":{}", arg);
+    }
+}