Add re-exec for server

This allows ASLR to re-randomize the address
space for every connection, preventing some
vulnerabilities from being exploitable by
repeated probing.

Overhead (memory and time) is yet to be confirmed.

At present this is only enabled on Linux. Other BSD platforms
with fexecve() would probably also work though have not been tested.

includes.h

@@ -127,6 +127,10 @@
 #include <sys/random.h>
 #endif
 
+#ifdef HAVE_SYS_PRCTL_H
+#include <sys/prctl.h>
+#endif
+
 #ifdef BUNDLED_LIBTOM
 #include "libtomcrypt/src/headers/tomcrypt.h"
 #include "libtommath/tommath.h"
@@ -171,6 +175,8 @@ typedef u_int32_t uint32_t;
 #include <dlfcn.h>
 #endif
 
+extern char** environ;
+
 #include "fake-rfc2553.h"
 
 #include "fuzz.h"