Fix cipher state chaining in OpenSSL back end

Fix cipher state chaining in OpenSSL back end

Make cipher state chaining work in the OpenSSL back end for des, des3,
and arcfour enc providers.  Subtleties:

* DES and DES3 have checks to avoid clobbering ivec with uninitialized
  data if there is no data to encrypt.
* Arcfour saves the OpenSSL cipher context across calls.  To protect
  against a caller improperly copying the state (which happens to work
  with other enc providers), a loopback pointer is used, as in GSSAPI.
* EVP_EncryptFinal_ex is unnecessary with stream ciphers and would
  interfere with cipher state chaining if it did anything, so just
  remove it.

ticket: 6665
target_version: 1.8
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23734 dc483132-0cff-0310-8789-dd5450dbe970