http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=84416
* doc/m4.texinfo (Maketemp): Change maketemp to refer to a new,
empty file rather than to a nonexistent file.  This closes a
common security hole.
* modules/m4.c (m4_maketemp): Implement the above, by using
mkstemp rather than mktemp.