Problem: Source files contain mixed tabs and spaces.

Solution: Convert to spaces and remove trailing whitespace in these files.

src/socket_base.cpp

@@ -322,7 +322,6 @@ int zmq::socket_base_t::setsockopt (int option_, const void *optval_,
         return -1;
     }
 
-
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
         EXIT_MUTEX();