Add rustfmt test for mut ref mut

Author: Jules-Bertholet

src/tools/rustfmt/tests/source/mut_ref_mut.rs

@@ -0,0 +1,10 @@
+#![feature(mut_ref_mut)]
+fn mut_ref_mut() {
+    if let Some(mut /*a*/ ref     /*def*/  mut     /*abc*/       state)=          /*abc*/foo{
+        println!(
+"asdfasdfasdf");	}
+
+if let Some(mut /*a*/ ref     /*def*/  /*mut*/       state)=          /*abc*/foo{
+    println!(
+"asdfasdfasdf");	}
+}

src/tools/rustfmt/tests/target/mut_ref_mut.rs

@@ -0,0 +1,10 @@
+#![feature(mut_ref_mut)]
+fn mut_ref_mut() {
+    if let Some(mut /*a*/ ref /*def*/ mut /*abc*/ state) = /*abc*/ foo {
+        println!("asdfasdfasdf");
+    }
+
+    if let Some(mut /*a*/ ref /*def*/  /*mut*/ state) = /*abc*/ foo {
+        println!("asdfasdfasdf");
+    }
+}