Prevent multiple "bootups" from occuring if the class is loaded twice

So this is based off your current tag, but not the latest commit.  The problem I'm having with your current tag is "PHP Fatal error: Cannot redeclare class Normalizer ..." because the autoloader of my app (Laravel 4/Composer) is loading utf8 twice, once for the app and once for the package I'm working on in the Laravel workbench.

I tried your most recent commit, but I get a "Fatal error: Class 'Normalizer' not found in /Users/reinhard/Work/BKWLD/Open Source/Laravel 4 Packages/vendor/patchwork/utf8/class/Patchwork/Utf8/bootup.php on line 292" when I try to install it.

This commit *does* fix my issue.