[gentoo-dev] dont use `which` in ebuilds

[Mike Frysinger]

please dont use the `which` program in your ebuilds ... this thing isnt even 
close to having standard behavior out there plus people can unmerge it :)

instead, since we require bash for our ebuilds, use the builtin `type -p` ... 
here's some easy examples:

-if which foo 2>/dev/null ; then
+if type -p foo > /dev/null ; then

-local fullpath=$(which foo 2>/dev/null)
+local fullpath=$(type -p foo)
-mike