Destroy the mutex in tls_config objects when tls_config_free is called.

Add a stub for pthread_mutex_destroy() for installers.

ok tb@

Add automatic threading initialization for libcrypto.

This implements automatic thread support initialization in libcrypto.
This does not remove any functions from the ABI, but does turn them into
no-ops. Stub implementations of pthread_mutex_(init|lock|unlock) are
provided for ramdisks.

This does not implement the new OpenSSL 1.1 thread API internally,
keeping the original CRYTPO_lock / CRYPTO_add_lock functions for library
locking. For -portable, crypto_lock.c can be reimplemented with
OS-specific primitives as needed.

ok beck@, tb@, looks sane guenther@