Thanks to John Fitzgibbon for initial patch.

Commit f77700aa, which fixes a compiler warning, also breaks the
behaviour of prepending ".<layer>" to basenames in --pxe-service: in
situations where the basename contains a ".", the ".<layer>" suffix is
erroneously added, and in situations where the basename doesn't contain
a ".", the ".<layer>" suffix is erroneously omitted.

A patch against the git HEAD is attached that inverts this logic and
restores the expected behaviour of --pxe-service.

Remove historic automatic inclusion of IDN support when
building internationalisation support. This doesn't
fit now there is a choice of IDN libraries. Be sure
to include either -DHAVE_IDN or _DHAVE_LIBIDN2 for
IDN support

This was causing confusion: DNSSEC queries would be sent to
servers for domains that don't do DNSSEC, but because of that status
the answers would be treated as answers to ordinary queries,
sometimes resulting in a crash.

This fixes build time warnings with POSIX.1-2008-aware c libraries.

Thanks to Stephan Zeisberg and
american fuzzy lop http://lcamtuf.coredump.cx/afl/

This reverts commit 88a77a78.

A least one client has been found which breaks with this change. Since
the use-case is not clear, I'm reverting the change, at least for now.