Problem: CURVE mechanism is unusable with chroot()

libsodium calls abort() when /dev/urandom can't be found
even if one creates ZeroMQ context before calling chroot()[1].

This happens because crypto gets initialized on handshake,
and at that moment the process is already chroot'ed.

Solution: initialize cryptographic libraries in ctx

randombytes_close() is already there in the destructor.

[1] https://download.libsodium.org/doc/usage/index.html

src/curve_server.hpp

@@ -129,7 +129,6 @@ namespace zmq
 
         void send_zap_request (const uint8_t *key);
         int receive_and_process_zap_reply ();
-        mutex_t sync;
     };
 
 }