[Bug #2331] Kernel#system の第一引数が書き換えられる

Bug #2331: Kernel#system e$B$NBh0l0z?t$,=q$-49$($i$l$ke(B
http://redmine.ruby-lang.org/issues/show/2331

e$B5/I<<Te(B: Kimura Yoshihiro
e$B%9%F!<%?%9e(B: Open, e$BM%@hEYe(B: Normal
ruby -v: ruby 1.8.7 (2009-06-12 patchlevel 174) [i386-mingw32]
e$B$*$h$Se(B [i386-mswin32]

mingw/mswin e$B4D6-$G!"e(Bsystem e$B$KEO$7$?%W%m%0%i%`J8;zNs$,e(B
/ e$B$+$ie(B \ e$B$K=q$-49$($i$l$^$9!#e(B

PROG = c:/ruby/bin/ruby.exe.freeze # e$B%Q%9L>$OG$0Ue(B
system(PROG, -v)
p PROG #=> c:\ruby\bin\ruby.exe

1.9e$B$G$OLdBj$J$$$h$&$G$9!#e(B