Add feature supports? :literal_equality.

Author: gkellogg

lib/rdf/mongo.rb

@@ -171,9 +171,10 @@ def initialize(options = {}, &block)
       # @see RDF::Mutable#insert_statement
       def supports?(feature)
         case feature.to_sym
-          when :graph_name   then true
-          when :atomic_write then true
-          when :validity     then @options.fetch(:with_validity, true)
+          when :graph_name        then true
+          when :atomic_write      then true
+          when :validity          then @options.fetch(:with_validity, true)
+          when :literal_equality  then true
           else false
         end
       end