implement 1.9.16 new api - updateBuildCustomFieldsValues

[lczub]

related TL github pull request https://github.com/TestLinkOpenSourceTRMS/testlink-code/pull/47

  /**
   * Update value of Custom Field with scope='design'
   * for a given Build
   *
   * @param struct $args
   * @param string $args["devKey"]: used to check if operation can be done.
   *                                if devKey is not valid => abort.
   *
   * @param string $args["buildid"]:
   * @param string $args["testprojectid"]:
   * @param string $args["customfields"]
   *               contains an map with key:Custom Field Name, value: value for CF.
   *               VERY IMPORTANT: value must be formatted in the way it's written to db,
   *               this is important for types like:
   *
   *               DATE: strtotime()
   *               DATETIME: mktime()
   *               MULTISELECTION LIST / CHECKBOX / RADIO: se multipli selezione ! come separatore
   *
   *
   *               these custom fields must be configured to be writte during execution.
   *               If custom field do not meet condition value will not be written
   *
   * @return mixed null if everything ok, else array of IXR_Error objects
   *
   * @access public
   */
  public function updateBuildCustomFieldsValues($args)