OpenSSL 1.0.0 has switched to generating PKCS#8 format private keys by
default. This change allows http.ListenAndServeTLS to work with either
types of keys.

See http://groups.google.com/group/golang-nuts/browse_thread/thread/84715b5f0c9e3c30/63a8a27b53e102a6

R=bradfitz
CC=golang-dev
https://golang.org/cl/5416059