Adds survivor machete.

As suggested by @John-Candlebury here:
http://smf.cataclysmdda.com/index.php?topic=8444.msg194374#msg194374.

An improved version of the machete, the survivor machete is an
autolearned craftable improvement that adds a couple points of damage
and a few techniques to the weapon.

Can occasionally spawn in survivor zed loot.