Specifying export_plugin as export option in argument handler should provide generic support

Problem/Motivation

In order to allow custom views argument handler settings to be exportable, an extra setting should simply be able to specify 'export' => 'export_plugin' and get automatic export of a simple key => value setting. It seems that this is what is intended, but the views_handler_argument code effectively excludes anything but 'default_argument_type' from using this method.

For example, if I wanted to specify an alternative to the '=' operator for a numeric handler (attached issue), I should be able to export that setting simply by including the following in method "option_definition()":

  function option_definition() {
    $options = parent::option_definition();
...
    $options['comparator'] = array(
      'default' => 'eq', 
      'export' => 'export_plugin',
    );

The export_plugin() method, while annotated as "* Generic plugin export handler. " prevents this by setting "type" to NULL unless the plugin is "default_argument_type". Because, in the following code, in class views_handler_argument, the variable $type is NULL unless $option is 'default_argument_type', and this overrides the default views_handler_argument::get_plugin($type = 'argument default', $name = NULL).

  function export_plugin($indent, $prefix, $storage, $option, $definition, $parents) {
    $output = '';
    if ($option == 'default_argument_type') {
      $type = 'argument default';
      $option_name = 'default_argument_options';
    }

    $plugin = $this->get_plugin($type);

Proposed resolution

Write the default export key = value option for any option that specifies "export_plugin" and has a non-array value for $option:

Change From:

    if ($plugin) {
      // Write which plugin to use.
      $output .= $indent . $prefix . "['$option'] = '$name';\n";

      // Pass off to the plugin to export itself.
      $output .= $plugin->export_options($indent, $prefix . "['$option_name']");
    }

to

    // Write default export_plugin info
    if(!is_array($name)) {
      $output .= $indent . $prefix . "['$option'] = '$name';\n";
    }
    if ($plugin) {
      // Pass off to the plugin to export itself.
      $output .= $plugin->export_options($indent, $prefix . "['$option_name']");
    }

Remaining tasks

1. (done)Write patch
2. Develop tests
3. Update patch if necessary

User interface changes

n/a

API changes

n/a

Data model changes

n/a