implement 1.9.20 changed api - getTestCasesForTestPlan - customfields

[lczub]

related TL pull request

• #203 from janLo/testplan_tc_custom_fields
• XMLRPC: Allow to fetch custom fields for testplan testcases

new optional args

• customfields

    /**
     * getTestCasesForTestPlan
     * List test cases linked to a test plan
     *
     * @param struct $args
     * @param string $args["devKey"]
     * @param int $args["testplanid"]
     * ....
     * @param array $args["customfields"]
     *             - optional can be a boolean or an array with the requested fields
     * @return mixed $resultInfo
     *
     * ...
     */
    public function getTestCasesForTestPlan($args) {