hygiene for for loops, if let, while let

and some unrelated test cleanups

src/librustc_typeck/check/mod.rs

@@ -1810,7 +1810,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // There is a possibility that this algorithm will have to run an arbitrary number of times
         // to terminate so we bound it by the compiler's recursion limit.
-        for _ in (0..self.tcx().sess.recursion_limit.get()) {
+        for _ in 0..self.tcx().sess.recursion_limit.get() {
             // First we try to solve all obligations, it is possible that the last iteration
             // has made it possible to make more progress.
             self.select_obligations_where_possible();