Changes

- Fixed an error in module_rehash_blocks() that didn't handle '-symbols.
- Removed some module depencies. Drupal will now run (sorta) even if there
  are no modules installed.
- Changed theme_link() to check if certain modules are installed before
  offering a link to them.

Todo
- Check all SQL queries to make sure they are addslashes'ed correctly.
- Check the effects of changing the PHP magic_quotes setting.
- Make the theme_link() function to be customizable either via the admin
  page and/or in the module itself.