* thread.cc: Finish the removal of the separate pthread_key
destructor list.
Remove all pthread_key_destructor and pthread_key_destructor_list
references throughout.
(pthread::exit): Call the new pthread_key interface to activate
destructors.
(pthread_key::keys): Change into a list.
(pthread_key::saveAKey): New method, used via forEach.
(pthread_key::restoreAKey): Ditto.
(pthread_key::destroyAKey): Ditto.
(pthread_key::fixup_before_fork): Use the List::forEach functionality.
(pthread_key::fixup_after_fork): Ditto.
(pthread_key::runAllDestructors): New method implementation.
(pthread_key::pthread_key): Use List::Insert rather than custom list
code.
(pthread_key::~pthread_key): Use List::Remove for the same reason.
* thread.h: Remove all pthread_key_destructor and
pthread_key_destructor_list references throughout.
(List): Move the interface above pthread_key in the header.
Use atomic operations during insert and delete.
(List::forEach): A generic interface for doing something on each node.
(pthread_key::runAllDestructors): New method, run all destructors.
(pthread_key::fork_buf): Make private.
(pthread_key::run_destructor): Ditto.
(pthread_key::saveAKey): New method for clearer source.
(pthread_key::restoreAKey): Ditto.
(pthread_key::destroyAKey): Ditto.
(MTinterface::destructors): Remove.