WindowsXPのInstant Rails環境でgem install rmagickをやると下記のエラーになる。 C:\InstantRails\rails_apps>gem install rmagick Building native extensions. This could take a while... ERROR: While executing gem ... (Gem::Installer::ExtensionBuildError) ERROR: Failed to build gem native extension. ruby gem_extconf.rb install rmagick sh configure gem_extconf.rb:38: undefined method `exitstatus' for nil:NilClass

