Ok, yeah, unless I'm misunderstanding your question,  `alias` and `alias_method` give the same results when placed directly in the module.  8 other AS tests throw errors like...

    TimeExtCalculationsTest#test_custom_date_format:
    ArgumentError: wrong number of arguments (1 for 0)
        /vagrant/rails/activesupport/test/core_ext/time_ext_test.rb:539:in `to_s'

which tells me that the `to_s` methods in the receiving classes are not being aliased.  So, the `self.included` callback seems to be the only way to go that I can think of.