Prepends a config array to the configs of the given extension.
string $name The name of the extension:
array $config The config to set:
public function prependExtensionConfig($name, array $config) {
  if (!isset($this->extensionConfigs[$name])) {
    $this->extensionConfigs[$name] = array();
  }
  array_unshift($this->extensionConfigs[$name], $config);
}