OTHER: Fix leak of coll operands in xmmsv_copy.
OTHER: Fix leak in collection test_client_save.
OTHER: Expose _int, _string, _value for coll attrs.
OTHER: Add support for full order attributes in order coll builder.
OTHER: Set coll attrs as dict in coll test utils.
OTHER: Make xmmsv_coll_t a part of xmmsv_t like list and dict.
OTHER: Add xmmsv_coll_is_type.
OTHER: Use xmmsv_(de)serialize to save/load collections.
FEATURE(2524): Bump src/lib/s4

* src/lib/s4 a9aff53...48487d9 (3):
  > OTHER: Add an order-builder to the s4_resultset_sort API.
  > OTHER: Remove unused _oplist_is_empty function.
  > OTHER: Add void arg to param-less funcs.
FEATURE(2524): Add field coalescing to Order collection.
FEATURE(2524): Accept list of strings for field attr of Order coll.
FEATURE(2524): Use coalescing sort in cli search.
OTHER: Fix broken medialib test.

Ordering the union by id breaks the component ordering
which is the ordering the test tries to exercise.