Fixes from M. Levinson:

1) Fixed typo in elinks option in etc/mhn.defaults.sh.
2) Added #include <sys/wait.h> to mhfixmsg.c.
3) Fixed seg fault when there's no corresponding profile entry
   for a message part in mhfixmsg.
4) If rename() fails in write_content() of mhfixmsg, attempt to
   copy and then remove the file.