IMPROVE: Move GemBox to more logical source location

tasks/mrbgem_spec.rake

@@ -158,4 +158,11 @@ module MRuby
 
     end # Specification
   end # Gem
+
+  GemBox = BasicObject.new
+  class << GemBox
+    def new(&block); block.call(self); end
+    def config=(obj); @config = obj; end
+    def gem(gemdir, &block); @config.gem(gemdir, &block); end
+  end # GemBox
 end # MRuby

tasks/mruby_build_gem.rake

@@ -1,11 +1,4 @@
 module MRuby
-  GemBox = BasicObject.new
-  class << GemBox
-    def new(&block); block.call(self); end
-    def config=(obj); @config = obj; end
-    def gem(gemdir, &block); @config.gem(gemdir, &block); end
-  end
-
   module LoadGems
     def gembox(gemboxfile)
       gembox = File.absolute_path("#{gemboxfile}.gembox", "#{MRUBY_ROOT}/mrbgems")