Adding script to enable clearing datastore.
Refactoring remove_kind to make while loop clearer.

Also stumbled upon other datastore gotchas (non-ancestor
deletes in a transaction) and added printing to indicate
what is being deleted.
Avoid extra URL-quoting of key name on upload.

Fixes #370.
Merge pull request #371 from tseaver/370-doubly_quoted_name_in_upload

#370: Avoid extra URL-quoting of key name on upload.
Merge pull request #369 from dhermes/clear-datastore-func

Adding script to enable clearing datastore.
Ideas commit for better (implicit) auth story in datastore.

Also
- Integrates this idea into the datastore regression tests.
- Creates a (temporarily ignored) cyclic import
- Has an uncovered statement that confuses nosetests
- Implements a friendlier (more gcloud-node like) version of
  allocated_ids
- DOES NOT update CONTRIBUTING to explain change to regression
  tests or ditch unneeded helper / environ code for regressions
- Creates a datastore cleanup script for when tests get
  broken