Loading fckeditor.config.js from theme path won't always work

Issue Summary

The code uses path_to_theme() to check and load the fckeditor.config.js from the default theme directory when the "use config from theme path" option is on.

However, due to the nature of how the path_to_theme() function works, the path returned may not be always the path to the actual theme of the site/user.

This will prevent the module from loading the theme specific fckeditor.config.js in a seemingly random way.

Please see #194098: path_to_theme() returns path to module that calls it for more info, and also the path_to_theme() function description.

Two solutions comes to mind:

1. Get the path to current theme using other methods. See http://drupal.org/node/194098#comment-1042283 and http://drupal.org/node/143885#comment-232587 for some alternative ways that may work. This may be also done using drupal_get_path('theme', $conf['theme_default'])
2. Replace the true/false switch with a text field where the admin can specify the URL path to the .js they want to use