Merges initial `options` into WCT's global configuration.

@param {Object} options The options to merge. See `browser/config.js` for a
reference.
function setup(options) {
    var childRunner = ChildRunner.current();
    if (childRunner) {
        _deepMerge(_config, childRunner.parentScope.WCT._config);
        // But do not force the mocha UI
        delete _config.mochaOptions.ui;
    }
    if (options && typeof options === 'object') {
        _deepMerge(_config, options);
    }
    if (!_config.root) {
        // Sibling dependencies.
        var root = scriptPrefix('browser.js');
        _config.root = basePath(root.substr(0, root.length - 1));
        if (!_config.root) {
            throw new Error('Unable to detect root URL for WCT sources. Please set WCT.root before including browser.js');
        }
    }
}