Missing lua_strlen in references

[Jorge <xxopxe@...>]

The function lua_strlen which appears mentioned in PiL
(http://www.lua.org/pil/24.2.2.html) is missing from the references.

The same with the printed PiL & Reference.


Jorge.

PS: i had to correct myself like a million times for typing libsub
instead of libusb, and now i ruin the release notice mail subject :(