Problem: reaper_t initialization reorder

Solution: initialize class variable in the same order as they are
defined.

src/reaper.cpp

@@ -35,8 +35,8 @@
 
 zmq::reaper_t::reaper_t (class ctx_t *ctx_, uint32_t tid_) :
     object_t (ctx_, tid_),
-    sockets (0),
     mailbox_handle(NULL),
+    sockets (0),
     terminating (false)
 {
     poller = new (std::nothrow) poller_t (*ctx_);