These files were pulled from the 1.6.3 release tarball.
This new version builds against OpenSSL version 1.1 which will be
the default in the new Debian Stable which is due to be released
RealSoonNow (tm).
Using libevent seems to have high peaks of file descriptor use,
which can cause failure to create fds in other parts of bitmonerod.
The fallback implementation seems to run fine in a significantly
tighter file descriptor limit.
Erik de Castro Lopo
Howard Chu
Riccardo Spagni
moneromooo-monero
Ben Boeckel