remove quotes on RUBYOPT on Windows

Quotes breaks things on Windows, too.
My RbConfig::CONFIG["host_os"] is mingw32.
My ruby is ruby-1.9.3-p392-i386-mingw32 (RubyInstaller for Windows).

When the quotes are included as in master, bundler/setup cannot be loaded.
After the quotes are removed, Rails (3.2.12) starts up normally.
The following is the log when executing 

    bundle exec rails s

with quotes included.

    C:/ruby-1.9.3-p392-i386-mingw32/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- bundler/setup (LoadError)
            from C:/ruby-1.9.3-p392-i386-mingw32/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
            from E:/myrailsproject/config/boot.rb:6:in `<top (required)>'
            from C:/ruby-1.9.3-p392-i386-mingw32/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
            from C:/ruby-1.9.3-p392-i386-mingw32/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
            from script/rails:5:in `<main>'