Make OrderedSet pickleable and deepcopyable
Make OrderedSet pickleable and deepcopyable

Users might want to pickle or deepcopy pymoca data structures, e.g.
AliasRelation. The linked list underlying the OrderedSet class (used by
AliasRelation and others) would produce max depth recursion errors with
the default behaviour, so we define methods __getstate__ and
__setstate__ to keep behaviour as expected.

jgoppert/pymola,jgoppert/pymola