Security fix for uninstall.php

“When using 'uninstall.php' the plugin should always check for the WP_UNINSTALL_PLUGIN constant, before executing. The WP_UNINSTALL_PLUGIN constant is defined by WordPress at runtime during a plugin uninstall, it will not be present if 'uninstall.php' is requested directly.”

http://codex.wordpress.org/Function_Reference/register_uninstall_hook