start_batch and end_batch add and remove the batch id from the
session. Modules wishing to do batch processing, just need to fire
the start_batch and end_batch events. Other modules that need to be
aware of batches (i.e. notifications) just check the session for "batch_id".
File_Structure_Test to make sure we don't regress.
According to the PHP docs, the "public" keyword is implied on static
functions, so remove it. Also, require private static functions to
start with an _.
http://php.net/manual/en/language.oop5.visibility.php
o Rename access::remove_group() to access::delete_group() for
consistency.
o Wrote more unit tests
o Tests found a bug in access::remove_item() .. yay!
