Provide a copy method in the patched S3 boto storage.

This results in better performance on file renames or clipboard pasting by
avoiding downloading and uploading under a separate name.
Fix NameError that happens if _delete_thumbnails fails while updating a files location.

Also provide a long explanation why update_location_on_storage overrides the default
transaction management offered by django's change_view.
atomic folder rename
Added test for folder renaming and renamed two existing tests to more appropriate names.
Added back bulk move and copy operations. These should work with the new overriden folder save
Improved performance by reducing the number of thumbnails that get generated.
Remove code duplication from thumbnail and icon generation.
Update documentation and remove unused import
Merge remote-tracking branch 'origin/update_files_on_folder_rename' into master_pbs.
Fixes #LUN-719 and #LUN-590 and some test fixes.

Also fixes a case with unit tests which assumes mkdtmp creates a root directory with
a single component.

Conflicts:
	filer/admin/folderadmin.py
	filer/storage.py