Update to FOF 2.3.4

# Executive summary

As I promised in the Joomla! Bug Sprint in Manchester last month, I'll keep updating FOF throughout the Joomla! 3 release cycle. This PR updates FOF to version 2.3.4. This version of FOF is fully backwards compatible to FOF 2.2.x which is already include in Joomla!.

# Testing instructions

After applying this patch make sure that the two factor authentication feature and post-installation messages components still work.

# Notes

This is a Joomla!-specific version with the prefix to all classes set to FOF (F-oh-F). The FOF project still maintains its own, separate version with an F0F (f-zero-f) class name prefix and different installation path (JPATH_LIBRARIES . '/f0f') which allows extension developers to use the latest and greatest FOF features and bug fixes as they see fit without having to replace the FOF version included with Joomla! itself.