Merge branch 'gem-duplication' of https://github.com/bovi/mruby into bovi-gem-duplication

tasks/mrbgem_spec.rake

@@ -169,6 +169,22 @@ module MRuby
       end
 
     end # Specification
+
+    class List < Array
+      def <<(gem)
+        fail ArgumentError.new("Don't find directory for this GEM") unless gem.respond_to? :dir
+        unless include?(gem)
+          super(gem)
+        else
+          # GEM was already added to this list
+        end
+      end
+
+      # we assume that a gem with the same directory is equal
+      def include?(gem)
+        detect {|g| g.dir == gem.dir }
+      end
+    end # List
   end # Gem
 
   GemBox = Object.new

tasks/mruby_build.rake

@@ -75,7 +75,7 @@ module MRuby
         @mrbc = Command::Mrbc.new(self)
 
         @bins = %w(mrbc)
-        @gems, @libmruby = [], []
+        @gems, @libmruby = MRuby::Gem::List.new, []
         @build_mrbtest_lib_only = false
 
         MRuby.targets[@name] = self