Fix check_dependencies.sh so it works on recent ubuntu linux as well as
mac.

Among many fixes, the psql postgres user test now users 'sudo', which
was not used in any of the tests before. I believe this is necessary for
ubuntu.
add 256-bit entropy paranoia to generateKeys

re: #125
don't send hmacKey to server when saving account
restore specific values to account object from server
add recordIndex to container payload to mitigate reordering attacks
implement deleteMessage transaction chunk type
implement message destruction
demonstrate message deletion in chat2 example
Remove challenge key DB columns; add srp columns
Add srp-client library
Generate SRP verifier on the client
challenge to SRP on server account creation
Use sha-256 for SRP
SRP fields for account retrieval
Add srp library to server
Expose BigInteger from SRPClient
change message schema to reflect move away from RSA
Finish SRP implementation
Whoops, genKey's callback has two args, not one.
Update srp-client to fix SHA256 hashing bug