Log Message:
Update ruby-httpclient to 2.7.1.

pkgsrc changes:
* Add completely support for pkg_alternatives (adding ALTERNATIVES).
* Remove ruby18 specific description in Makefile.

Changes in 2.7.1

Jan 1, 2016 - version 2.7.1

* Changes

  - Symbol aware header key comparison
    Normalizes symbol to String for header key.
    https://github.com/nahi/httpclient/issues/278

  - Show warning message only once
    Added HTTPClient::Util.warning that cached warning message and supress
    the message if it's already dumped.
  - Use Timeout.timeout instead of Kernel.timeout that is deprecated from
    ruby 2.3.0.

* Bug fixes

  - [JRuby] Set ssl_version properly