Sort enabled adapter extensions in schema dump

The list of enabled adapter extensions in the schema dump isn't
sorted by default, so it may happen that the sorting changes
over time. If you're using a VCS, a change to the sorting results
in a diff without any real change. Sorting the list should solve
this problem.

activerecord/lib/active_record/schema_dumper.rb

@@ -85,7 +85,7 @@ HEADER
         extensions = @connection.extensions
         if extensions.any?
           stream.puts "  # These are extensions that must be enabled in order to support this database"
-          extensions.each do |extension|
+          extensions.sort.each do |extension|
             stream.puts "  enable_extension #{extension.inspect}"
           end
           stream.puts

activerecord/test/cases/schema_dumper_test.rb

@@ -301,6 +301,20 @@ class SchemaDumperTest < ActiveRecord::TestCase
         assert_no_match "# These are extensions that must be enabled", output
         assert_no_match %r{enable_extension}, output
       end
+
+      def test_schema_dump_includes_extensions_in_alphabetic_order
+        connection = ActiveRecord::Base.connection
+
+        connection.stubs(:extensions).returns(["hstore", "uuid-ossp", "xml2"])
+        output = perform_schema_dump
+        enabled_extensions = output.scan(%r{enable_extension "(.+)"}).flatten
+        assert_equal ["hstore", "uuid-ossp", "xml2"], enabled_extensions
+
+        connection.stubs(:extensions).returns(["uuid-ossp", "xml2", "hstore"])
+        output = perform_schema_dump
+        enabled_extensions = output.scan(%r{enable_extension "(.+)"}).flatten
+        assert_equal ["hstore", "uuid-ossp", "xml2"], enabled_extensions
+      end
     end
   end