Fixes for emacs integration tests (resolves #710)

Fixes two tests that were consistently failing on OSX:

 1 - "Test rename refactoring over multiple files."
This test was failing for reasons detailed in issue #710. My fix is small and localized, leaving the larger question of canonicalization for another pass. In any case, I think it's reasonable that reverting a buffer should not alter buffer-file-name.

 2 - "Test deleting file and reloading."
This test was hanging because the (find-file...) call was not triggering a typecheck as it should have, because the ensime minor mode was not engaged. Added the hook in the startup script. (Was this passing on linux/windows?)

All (enabled)integrations passing for me now.
It seems that advice-add was introduced recently. This works for me:
```elisp
(defadvice message (before ensime-log-to-file (format-string &rest args))
  (let ((text (when format-string
                 (format "Msg: %s\n" (apply 'format format-string args)))))
    (write-region text nil ensime-test-log-file 'append)
    text))
(ad-activate 'message)
```