Multiple bug fixes.
- fix CVE-2015-4000 - prevent the logjam attack on client - restrict
the DH key size to at least 768 bits (limit will be increased in future)
- drop the AES-GCM restriction of 2^32 operations because the IV is
always 96 bits (32 bit fixed field + 64 bit invocation field)
- fix regression in RAND locking (#1225994)