Better integration of libevent in build system.

Since event.h is not part of tinc, we include it in have.h were all other
system header files are included.  We also ensure -levent comes before -lgdi32
when compiling with MinGW, apparently it doesn't work when the order is
reversed.

have.h

@@ -37,6 +37,7 @@
 #else
 #define WINVER WindowsXP
 #endif
+#define WIN32_LEAN_AND_MEAN
 #include <w32api.h>
 #include <windows.h>
 #include <ws2tcpip.h>
@@ -179,4 +180,8 @@
 #include <netinet/if_ether.h>
 #endif
 
+#ifdef HAVE_EVENT_H
+#include <event.h>
+#endif
+
 #endif /* __TINC_SYSTEM_H__ */

m4/libevent.m4

@@ -27,7 +27,7 @@ AC_DEFUN([tinc_LIBEVENT],
   )
 
   AC_CHECK_LIB(event, event_init,
-    [LIBS="$LIBS -levent"],
+    [LIBS="-levent $LIBS"],
     [AC_MSG_ERROR("libevent libraries not found.")]
   )
 ])

src/net.h

@@ -21,8 +21,6 @@
 #ifndef __TINC_NET_H__
 #define __TINC_NET_H__
 
-#include <event.h>
-
 #include "ipv6.h"
 #include "cipher.h"
 #include "digest.h"

src/node.h

@@ -21,8 +21,6 @@
 #ifndef __TINC_NODE_H__
 #define __TINC_NODE_H__
 
-#include <event.h>
-
 #include "splay_tree.h"
 #include "cipher.h"
 #include "connection.h"