- add closefrom fallback for OS X / Linux systems, extracted from sudo,
but without the optimized versions, since they cannot work in a
chroot environment (and we're not performance critical here.)
- enable detecting libtls
- conditionally enable https constraint support

Fixes #3, thanks to @gitisihara for providing the initial patch and
testing.

Remove dependency on libcrypto, include hash headers in a nicer way.

First attempt at building a new OpenNTPD portable project, based on the
latest OpenBSD source.