test for setsid function

configure.in

@@ -127,7 +127,7 @@ AC_C_INLINE
 AC_CHECK_SIZEOF(unsigned long)
 AC_CHECK_SIZEOF(unsigned int)
 AC_CHECK_TYPE(ptrdiff_t,int)
-AC_CHECK_FUNCS(unsetenv alphasort scandir strerror strsignal strtoul)
+AC_CHECK_FUNCS(unsetenv alphasort scandir strerror strsignal strtoul setsid)
 AC_CHECK_FUNCS(vsnprintf lchown snprintf)
 AC_CHECK_HEADERS(sys/cdefs.h syslog.h stddef.h)
 AC_CHECK_HEADERS(error.h)