Issue #13992: The trashcan mechanism is now thread-safe. This eliminates

Issue #13992: The trashcan mechanism is now thread-safe.  This eliminates
sporadic crashes in multi-thread programs when several long deallocator
chains ran concurrently and involved subclasses of built-in container
types.

Note that the trashcan functions are part of the stable ABI, therefore
they have to be kept around for binary compatibility of extensions.