* expr.c (make_expr_symbol): If operator is O_symbol and X_add_number is zero,

* expr.c (make_expr_symbol): If operator is O_symbol and X_add_number is zero,
just return the symbol.  If operator is O_constant, resolve the symbol's value
before returning.
(operand): Permit use of "[]" for grouping.
(clean_up_expression): For difference of two symbols in the same frag, add the
difference of their offsets into X_add_number.
(expr): Reduce difference of two symbols in same frag to their difference.