def files
    # DO NOT CHANGE TO ||= ! This is not a normal accessor. (yes, it sucks)
    @files = [@files,
              @test_files,
              add_bindir(@executables),
              @extra_rdoc_files,
              @extensions,
             ].flatten.uniq.compact
  end
#
Files included in this gem.  You cannot append to this accessor, you must
assign to it.

Only add files you can require to this list, not directories, etc.

Directories are automatically stripped from this list when building a gem,
other non-files cause an error.