Deallocation functions in zmq.h and msg_t class are consistent.

The two functions had different calling conventions (C vs. C++).
It is fixed now.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/msg.cpp

@@ -68,7 +68,7 @@ int zmq::msg_t::init_size (size_t size_)
     return 0;
 }
 
-int zmq::msg_t::init_data (void *data_, size_t size_, zmq_free_fn *ffn_,
+int zmq::msg_t::init_data (void *data_, size_t size_, msg_free_fn *ffn_,
     void *hint_)
 {
     u.lmsg.type = type_lmsg;

src/msg.hpp

@@ -26,6 +26,14 @@
 #include "config.hpp"
 #include "atomic_counter.hpp"
 
+//  Signature for free function to deallocate the message content.
+//  Note that it has to be declared as "C" so that it is the same as
+//  zmq_free_fn defined in zmq.h.
+extern "C"
+{
+    typedef void (msg_free_fn) (void *data, void *hint);
+}
+
 namespace zmq
 {
 
@@ -43,13 +51,10 @@ namespace zmq
             shared = 128
         };
 
-        //  Signature for free function to deallocate the message content.
-        typedef void (free_fn_t) (void *data, void *hint);
-
         bool check ();
         int init ();
         int init_size (size_t size_);
-        int init_data (void *data_, size_t size_, free_fn_t *ffn_,
+        int init_data (void *data_, size_t size_, msg_free_fn *ffn_,
             void *hint_);
         int init_delimiter ();
         int close ();
@@ -82,7 +87,7 @@ namespace zmq
         {
             void *data;
             size_t size;
-            free_fn_t *ffn;
+            msg_free_fn *ffn;
             void *hint;
             zmq::atomic_counter_t refcnt;
         };