Fix issue 861: configure.sh fails on mac os x
Merge pull request #878 from benemorius/fix_configure_script_for_mac

Fix issue 861: configure.sh fails on mac os x
Move exception out of crypto_util
Refactor guid exists check
Merge pull request #880 from hoffmabc/decline-legacy-msgs

Move exception out of crypto_util
Streamline _on_raw_message.
Simplify signature verification.

* We cannot avoid loading the data before verifying because it contains
  the pubkey.
Extract message deserialization.

* Dump validate_signature.
Verify the handshake type.
Split deserialization into many methods.

* Drop is_handshake.
No need to keep the keys as attributes.

* The keys can always be derived from the cryptor, though they will be
  in pyelliptic format.