curl: libressl support

New ground has been broken. New seeds have been sowed, etc etc. This
makes the necessary changes to LibreSSL and cURL to enable the latter
to be built with the former. This has been supported upstream for the
last 3 months, and cURL officially supports LibreSSL
[now](http://daniel.haxx.se/blog/2014/08/05/libressl-vs-boringssl-for-cu
rl/) and [has done](http://curl.haxx.se/changes.html) since 7.38.0. A
recompile of LibreSSL and cURL is necessary if you wish to adopt this
locally, but the dependents of cURL should not need to be recompiled.