Add global init/exit points, to do crypto initialization in one place.

By Lars Nordin.

src/session.c

@@ -457,7 +457,8 @@ libssh2_session_init_ex(LIBSSH2_ALLOC_FUNC((*my_alloc)),
         session->api_block_mode = 1; /* blocking API by default */
         _libssh2_debug(session, LIBSSH2_TRACE_TRANS,
                        "New session resource allocated");
-        libssh2_crypto_init();
+        if (!libssh2_initialized)
+            libssh2_init(0);
     }
     return session;
 }