merge revision(s) 41600: [Backport #8058]

	* test/rubygems/test_gem_installer.rb (test_install_extension_flat):
	  use ruby in build directory in case ruby is not installed.
	  [ruby-core:53265] [Bug #8058]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@41668 b2dd03c8-39d4-4d8f-98ff-823fe69b080e