add(update_ebuilds): A little script for fetching upstream ebuilds.

Meant to add this last week... It can either pull from Gentoo CVS or a
local directory (in case you rsynced the whole portage tree). Just name
a package by pkg-cat/name and it will update portage-stable.
Merge pull request #4 from marineam/update_ebuilds

add(update_ebuilds): A little script for fetching upstream ebuilds.