Convert old-style for loops to new-style

Most could use the each method, but because of the hack used to
disambiguate old- and new-style loops, some had to use vec::each.

(This hack will go away soon.)

Issue #1619

src/librustsyntax/fold.rs

@@ -338,7 +338,7 @@ fn noop_fold_pat(p: pat_, fld: ast_fold) -> pat_ {
           }
           pat_rec(fields, etc) {
             let mut fs = [];
-            for f: ast::field_pat in fields {
+            for fields.each {|f|
                 fs += [{ident: f.ident, pat: fld.fold_pat(f.pat)}];
             }
             pat_rec(fs, etc)