This patch enhances the uninstall process

I just made a patch that removes any leftover items in the variable table, checks for the existence of table names before attempting deletion, and clears the drupal cache during the uninstall in order to prevent anon user ghosted nodes and the associated warnings they'd receive.

I also added a friendly message informing the user of everything that was successfully completed during the uninstall process.

The original functionality that removes multichoice data from node and node_revisions has not been altered.