[Bug #1957] NKF.nkf でシフトJISの "\e" が "" に変換される

e$B%A%1%C%He(B #1957 e$B$,99?7$5$l$^$7$?!#e(B (by Masahiro T.)

e$B8D?ME*$K$O$3$N$^$^$G$b:$$k$3$H$O$J$$$G$9!#e(B
e$B%P%[email protected]$C$?$N$G$H$j$"$($:EPO?$7$^$7$?!#e(B
e$B$J$N$G!"$3$N$^$^%/%m!<%:$7$F$b$i$C$F$b9=$$$^$;$s!#e(B

http://redmine.ruby-lang.org/issues/show/1957