Use string literals in printf style calls so gcc's -Wformat works.

ok tedu@, miod@
Add support for automatic ephemeral EC keys.

This allows an SSL server to enable ECDHE ciphers with a single setting,
which results in an EC key being generated using the first preference
shared curve.

Based on OpenSSL with inspiration from boringssl.

ok miod@
Bump minor version for ECDH auto.

While there are no additional symbols, there is an additional command that
clients will potentially depend on.