LibreSSL 2.0 (new formula)

Add a formula for the [first portable release](http://marc.info/?l=openbsd-tech&m=140510291304119&w=2) of [LibreSSL](http://www.libressl.org/), OpenBSD's fork of OpenSSL.
We can just remove the option and always run `make check`, as we do for openssl and other crypto software.