Add explicit casts to quiet warnings in libefi

Sponsored by:	The FreeBSD Foundation
Wakeup only one thread of added in r263978i at a time.

This slightly reduces lock congestion between threads.

Submitted by:	trasz
Fix NFS deadlock vulnerability. [SA-14:05]

Fix "Heartbleed" vulnerability and ECDSA Cache Side-channel
Attack in OpenSSL. [SA-14:06]