Zend\Http: Unit tests for multi-line headers

As per http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html and the original issue #5608

Notes:
  * http://stackoverflow.com/questions/8627263/multi-line-http-headers-confusion
  * https://github.com/joyent/http-parser/pull/45
  * also, pecl_http's http_parse_header() function, which also respects the LWS for mulit-line