fixes #439 exposing nn_sleep() was a mistake

Revert "fixes #437 inconsistent DLL linkage for nn_sleep"
This reverts commit 3d978156c04bd75052deaa1726f2b4b5bccc989c.

Revert "Allowed nn_sleep to be exported on Windows."
This reverts commit e3588bc987f60fa841c153df89a70c7a3f1eb02c.
diff --git a/Makefile.am b/Makefile.am
index 3971922..41cf5b3 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -141,6 +141,7 @@
     src/utils/random.c \
     src/utils/sem.h \
     src/utils/sem.c \
+    src/utils/sleep.h \
     src/utils/sleep.c \
     src/utils/stopwatch.h \
     src/utils/stopwatch.c \
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index db1d995..ad23565 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -126,6 +126,7 @@
     utils/random.c
     utils/sem.h
     utils/sem.c
+    utils/sleep.h
     utils/sleep.c
     utils/thread.h
     utils/thread.c
diff --git a/src/core/poll.c b/src/core/poll.c
index b2342a8..cb61ddf 100644
--- a/src/core/poll.c
+++ b/src/core/poll.c
@@ -26,6 +26,7 @@
 
 #include "../utils/win.h"
 #include "../utils/fast.h"
+#include "../utils/sleep.h"
 #include "../utils/err.h"
 
 int nn_poll (struct nn_pollfd *fds, int nfds, int timeout)
diff --git a/src/nn.h b/src/nn.h
index ec5d12a..0271c03 100644
--- a/src/nn.h
+++ b/src/nn.h
@@ -357,7 +357,6 @@
 NN_EXPORT int nn_recv (int s, void *buf, size_t len, int flags);
 NN_EXPORT int nn_sendmsg (int s, const struct nn_msghdr *msghdr, int flags);
 NN_EXPORT int nn_recvmsg (int s, struct nn_msghdr *msghdr, int flags);
-NN_EXPORT void nn_sleep (int milliseconds);
 
 /******************************************************************************/
 /*  Socket mutliplexing support.                                              */
diff --git a/src/utils/sleep.c b/src/utils/sleep.c
index eee3ec2..6ae30bc 100644
--- a/src/utils/sleep.c
+++ b/src/utils/sleep.c
@@ -20,7 +20,7 @@
     IN THE SOFTWARE.
 */
 
-#include "../nn.h"
+#include "sleep.h"
 #include "err.h"
 
 #ifdef NN_HAVE_WINDOWS
diff --git a/src/utils/sleep.h b/src/utils/sleep.h
new file mode 100644
index 0000000..de943c4
--- /dev/null
+++ b/src/utils/sleep.h
@@ -0,0 +1,30 @@
+/*
+    Copyright (c) 2012 Martin Sustrik  All rights reserved.
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom
+    the Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+    IN THE SOFTWARE.
+*/
+
+#ifndef NN_SLEEP_INCLUDED
+#define NN_SLEEP_INCLUDED
+
+/*  Platform independent implementation of sleeping. */
+
+void nn_sleep (int milliseconds);
+
+#endif
diff --git a/tools/tcpmuxd.c b/tools/tcpmuxd.c
index 00209f8..eb1401a 100644
--- a/tools/tcpmuxd.c
+++ b/tools/tcpmuxd.c
@@ -23,6 +23,7 @@
 #include "../src/nn.h"
 
 #include "../src/utils/err.h"
+#include "../src/utils/sleep.h"
 
 #include <stdlib.h>
 #include <stdio.h>