Add simple cache to Bundler.load_gemspec

lib/bundler.rb

@@ -230,6 +230,11 @@ def read_file(file)
     end
 
     def load_gemspec(file)
+      @gemspec_cache ||= {}
+      @gemspec_cache[File.expand_path(file)] ||= load_gemspec_uncached(file)
+    end
+
+    def load_gemspec_uncached(file)
       path = Pathname.new(file)
       # Eval the gemspec from its parent directory
       Dir.chdir(path.dirname.to_s) do