Standardize on dhe ([rt.openssl.org #3203])

See: https://rt.openssl.org/Ticket/Display.html?id=3203

The relevant RFCs and other implementations refer to Diffie-Hellman
ephemeral key exchange as "DHE" (and its elliptic curve variant as
"ECDHE"). OpenSSL uses this terminology in some places, but it also
uses "EDH" and "EECDH" in others. This confusion makes selecting
these key exchange mechanisms harder for administrators to understand.

For example, there is a ciphersuite that openssl calls
EDH-RSA-DES-CBC3-SHA, and another one called DHE-RSA-AES128-SHA, whose
only difference is the choice of the cipher.

Another example is that "openssl ciphers -v EECDH" emits no
ciphersuites named with "EECDH" in them, but rather produces all
"ECDHE" strings. And "openssl ciphers -v ECDHE" fails with "Error in
cipher list".

See: Message-ID:
<1387528669-26823-1-git-send-email-dkg@fifthhorseman.net>, e.g. at
http://thread.gmane.org/gmane.comp.encryption.openssl.devel/23577/focus=23579
and following messages in that thread.