Clear SDES crypto info only after we received a first valid SRTP packet
Add Skein hash and MAC to ZRTP

ZRTP can now negotiate Skein as Hash and MAC algorithm. We can use Skein as
replacment to the old SHA256 and SHA384 hash and HMAC algorithms.
Use correct hash context functions
Handle the NIST algorithm selection
Resolve a merge conflict

Conflicts:
	clients/tivi/CtZrtpStream.cpp
Merge branch 'skein' into develop
Merge branch 'develop'