[ITK] http support on midas3.kitware.com

[Matt McCormick]

Hi folks,

The server that hosts ITK data -- midas3.kitware.com now only supports
https, and does not support downloading via the http protocol. This
may result in build errors like:

  error: downloading
  'http://midas3.kitware.com/midas/download/bitstream/457653/castxml-linux.tar.gz'
  failed

    status_code: 1
    status_string: "Unsupported protocol"
    log:   Trying 192.168.120.111...

  Connected to midas3.kitware.com (192.168.120.111) port 80 (#0)

To address this error, the CMake client needs OpenSSL support. Newer
binaries from cmake.org have this support.  When building from source,
this is not enabled by default -- enable the configuration option
CMAKE_USE_OPENSSL.

Matt