+ make the add items to the temporary queue public

  - this is @brummett's first suggestion in github's genome pull request
    301.

    https://github.com/genome/genome/pull/301
+ make an explicit debug message when the temp queue is empty
+ remove needless pass statement in test
+ refactor for loop in show_temporary_input_files_queue

  - this is @brummett's second suggestion in github's genome pull request 301

    https://github.com/genome/genome/pull/301