Fix a horrible scoping/associativity bug.

`1 as $x | . | $x` didn't compile, as it was parsed as

    (1 as $x | .) | $x

where `$x` is undefined, rather than as

    1 as $x | (. | $x)

parser.y

@@ -75,7 +75,7 @@ struct lexer_param;
 
  /* revolting hack */
 %left ';'
-%left '|'
+%right '|'
 %left ','
 %right "//"
 %nonassoc '=' SETPIPE SETPLUS SETMINUS SETMULT SETDIV SETDEFINEDOR