internal/catmsg: added varint implementation the catmsg package contains functionality local to x/text internal related to the catalog package. Change-Id: Iba503cf7dd67ad82973727bc096e4732d4dcf56b Reviewed-on: https://go-review.googlesource.com/41330 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Nigel Tao <nigeltao@golang.org>