accept naked exprs with commas in pattern arms

pretty printing will use them, but indentation is slightly off
if the expr is long

src/libsyntax/ast_util.rs

@@ -588,6 +588,13 @@ fn view_path_id(p: @view_path) -> node_id {
     }
 }
 
+fn lone_block_expr(blk: blk) -> option<@ast::expr> {
+    if blk.node.view_items.len() != 0 { ret none; }
+    if blk.node.stmts.len() != 0 { ret none; }
+    if blk.node.rules != default_blk { ret none; }
+    ret blk.node.expr;
+}
+
 // Local Variables:
 // mode: rust
 // fill-column: 78;