v6.60.4. Improvement. Bugfix.

- v6.60.4 January 27, 2014
	- Implemented `304 Not Modified` header
	- Fixed some `date` and `stat` errors (regression since v6.60.0)
		- Thanks to [Anton Wilhelm](https://github.com/timaschew) for [pull
request #787](https://github.com/bevry/docpad/pull/787)
		- Thanks to [Ivan Klimchuk](https://github.com/Alroniks) for [pull
request #781](https://github.com/bevry/docpad/pull/781)