Wait and retry downloads when resource not consistent

[dleehr]

Issue #149 causes uploads to be retried if 404 + resource_not_consistent is encountered on creating an upload. It's also possible to get a 404 + resource_not_consistent from /files/:id/url (get_file_url).

Currently, attempting to download a project with files that are not yet consistent results in:

$ ddsclient download -p test_project

Error 404 on /files/1c0396f6-6737-459f-b24b-9455dac398a9/url
Reason:resource changes are still being processed by system
Suggestion:this is a temporary state that will eventually be resolved by the system; please retry request