the devmanual does not discuss pkg_info or even list it as available. http://devmanual.gentoo.org/ebuild-writing/functions/
Because it isn't.
it's in portage already thus it should be documented in the devmanual
I'd suggest removing what's in portage and replacing it with something that doesn't have several nasty design flaws first... Implementation before design is not the way to get good results.
this not the forum for such things you wish to have things change, follow up to the gentoo-dev thread a while back which had this functionality merged
Included in r170
Anything left to do here? The page seems to be available at http://devmanual.gentoo.org/ebuild-writing/functions/pkg_info/index.html