code: function _gpfHttpSetRequestImplIf (host, httpRequestImpl) {
      var result = _gpfHttpRequestImpl;
      if (host === _gpfHost) {
          _gpfHttpRequestImpl = httpRequestImpl;
      }
      return result;
  }
docs: Set the http request implementation if the host matches
  
  @param {String} host host to test, if matching with the current one, the http request implementation is set
  @param {Function} httpRequestImpl http request implementation function
  @return {Function} Previous host specific implementation
  @since 0.2.6