This package provides a few useful collection objects. Note that it used to be
named collections, but without absolute imports (PEP 328), this
precluded using the standard library's collections module.
For compatibility, it provides a clone of the Python
bbcollections.defaultdict for use in Python-2.4. In later versions, this
is simply a reference to the built-in defaultdict, so buildbot code can
simply use buildbot.util.collections.defaultdict everywhere.
It also provides a KeyedSets class that can represent any numbers of
sets, keyed by name (or anything hashable, really). The object is specially
tuned to contain many different keys over its lifetime without wasting memory.
See the docstring for more information.