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/rustc/util/common.rs

@@ -46,7 +46,7 @@ fn field_expr(f: ast::field) -> @ast::expr { ret f.node.expr; }
 
 fn field_exprs(fields: [ast::field]) -> [@ast::expr] {
     let mut es = [];
-    for f: ast::field in fields { es += [f.node.expr]; }
+    for fields.each {|f| es += [f.node.expr]; }
     ret es;
 }