Problem: zmq_sendiov/zmq_recviov not Deprecated

Solution:
As preparation for 4.2 release, move the zmq_sendiov and zmq_recviov API
methods under the Deprecated Methods section.

Note: the actual methods have NOT been deprecated yet, functionally speaking
however it is good to let API users know early. Moreover, these methods were
not ever considered stable, at least according to src/zmq.h, and have no
associated man pages.

include/zmq.h

@@ -451,7 +451,9 @@ ZMQ_EXPORT int zmq_has (const char *capability);
 ZMQ_EXPORT int zmq_device (int type, void *frontend, void *backend);
 ZMQ_EXPORT int zmq_sendmsg (void *s, zmq_msg_t *msg, int flags);
 ZMQ_EXPORT int zmq_recvmsg (void *s, zmq_msg_t *msg, int flags);
-
+struct iovec;
+ZMQ_EXPORT int zmq_sendiov (void *s, struct iovec *iov, size_t count, int flags);
+ZMQ_EXPORT int zmq_recviov (void *s, struct iovec *iov, size_t *count, int flags);
 
 /******************************************************************************/
 /*  Encryption functions                                                      */
@@ -485,11 +487,6 @@ ZMQ_EXPORT void zmq_atomic_counter_destroy (void **counter_p);
 /*  page, and (b) write a test case in tests.                                 */
 /******************************************************************************/
 
-struct iovec;
-
-ZMQ_EXPORT int zmq_sendiov (void *s, struct iovec *iov, size_t count, int flags);
-ZMQ_EXPORT int zmq_recviov (void *s, struct iovec *iov, size_t *count, int flags);
-
 /*  Helper functions are used by perf tests so that they don't have to care   */
 /*  about minutiae of time-related functions on different OS platforms.       */