New implementation of finer lock grain in _hashlibopenssl: only create 
the lock at the first update with more than 8 KB bytes. Object 
creation/deallocation is faster if we hash less than 8 KB.

Changes between hashopenssl_threads-4.diff and my new patch: fix the 
deadlock in ENTER_HASHLIB() (for the GIL) without speed change 
(because we don't change the GIL state if we don't use a lock).

Changes between py3k trunk and my new patch:
 - release the GIL with large byte string => faster with multiple CPUs
 - fix EVP_get_block_size() and EVP_get_digest_size(): the context was 
not protected by the lock!