Fix libcloud url idempotency 133

[ljluestc]

Made LibCloudStorage.url() in storages/backends/apache_libcloud.py idempotent by avoiding unnecessary API calls for non-CDN providers (e.g., Google Cloud Storage) and handling empty paths (e.g., {% static '' %}), addressing issue #133. Fixed storages.utils.clean_name to preserve empty strings, resolving invalid URLs in Google Cloud Storage (issue #132). The url() method now returns the base bucket URL for empty paths without querying the storage API and skips _get_object for drivers without get_object_cdn_url. Tests verify behavior across providers, including GCS and S3, and empty path handling. Documentation and changelog updated.

Key Changes

• Updated LibCloudStorage.url():

  • Handles empty name by returning base bucket URL (e.g., https://storage.googleapis.com/test-bucket/) without API calls.
  • Checks for get_object_cdn_url before calling _get_object, avoiding unnecessary API requests for non-CDN drivers.
  • Returns None for nonexistent objects in CDN mode.

• Fixed storages.utils.clean_name:

  • Preserves empty strings ('') to prevent transformation to '.', fixing 302 redirects in GCS (django-storages generates invalid Google Cloud Storage URL #132).

• Added tests in tests/test_apache_libcloud.py:

  • Verified base URL generation for empty paths without API calls (GCS, S3).
  • Tested URL construction for existing and nonexistent objects.
  • Confirmed CDN-enabled driver behavior.
  • Ensured clean_name('') returns empty string.