o Code simplification and refactoring:
    - Unconditionally use OpenSSL's AES implementation instead of our
      old built-in one. OpenSSL's AES has been better for a while, and
      relatively few servers should still be on any version of OpenSSL
      that doesn't have good optimized assembly AES.

  o Major features:
    - Use OpenSSL's EVP interface for AES encryption, so that all
      AES operations can use hardware acceleration (if present).
      Resolves issue #4442.