Fix: Log entries are written twice

During plugin bootstrap phase, a call to CakeLog::critical() maybe made
(due to missing plugin) when the Log engine has not been configured.

This causes entries to be written twice and a file `tmp/logs/.log`
to be created incorrectly.

Conflicts:
	Config/bootstrap.php

See: croogo/croogo@09d1934
Remove 'Log' from CakeLog engine names

See:
	http://book.cakephp.org/2.0/en/appendices/2-4-migration-guide.html#logging
	croogo/croogo@239a4ba