Document or resolve all pragma no covers in non-test/demo code.

Current offenders as of 61232de

datastore.key.Key.parent
storage.acl.ACL.save
storage.bucket.Bucket.new_key (Py3k related,
though we could remove basestring from globals)
storage.connection.Connection.new_bucket (Py3k related,
though we could remove basestring from globals)
storage.connection.Connection.generate_signed_url
storage.iterator.Iterator.get_items_from_response
storage.key.Key.generate_signed_url
storage.key.Key.get_contents_to_file

The harmless bunch are __repr__ though they would be easy to test.

Deferring the 'Bucket.new_key' and 'Connection.new_bucket' fixes until we are handling #91.

The 'Connection.generate_signed_url' uses '_Monkey' to stub out the 'crypto', 'RSA', 'PKCS_v1_5' and 'SHA256' names (doing it for the Key method is simpler, as it just delegates to its connection).

Trying to cover 'repr' is generally pointless: there is no interesting logic, and they often contain hard-to-test ephemeral values. We could excluded them repo-wide via a '.coveragerc' file, as in the example in the coverage docs:

http://nedbatchelder.com/code/coverage/config.html

Done in a3737e6.