[Bug #409] Can't modify frozen ... $B$N7?(B

[Shyouhei_U]

e$B%A%1%C%He(B #409 e$B$,99?7$5$l$^$7$?!#e(B (by Shyouhei U.)

e$B%+%F%4%je(B coree$B$+$ie(BDOCe$B$KJQ99e(B
e$BM%@hEYe(B Normale$B$+$ie(BLowe$B$KJQ99e(B

e$B0U?^$5$l$F$$$k$J$i$^$"$$$$$s$8$c$J$$$G$7$g$&$+!#e(B

e$B$?$@!":#$N$^$^$@$H%P%0$H6hJL$,$D$+$J$$$N$G$I$3$+$K%I%-%e%a%s%H$7$F$*$/$Y$-$G$7$g$&!#e(B

http://redmine.ruby-lang.org/issues/show/409