Skip extra slash test on 1.8.7 due to @d0eb6aed

Author: drbrain

test/rubygems/test_gem_package.rb

@@ -335,6 +335,7 @@ def test_install_location_absolute
   end
 
   def test_install_location_extra_slash
+    skip 'no File.realpath on 1.8' if RUBY_VERSION < '1.9'
     package = Gem::Package.new @gem
 
     file = 'foo//file.rb'