Also standardize on 'utf8' as encoding name.
Apparently either is acceptable.

The user, because it is a StringProperty,
must be of type unicode in order to handle
Unicode correctly.  It must *not* have type string.

The desc, because it is a BlobProperty, must
be of type string in order to handle Unicode correctly.
It must *not* have type unicode.

Yay encoding type pedantry without static typing.

R=adg, mattn.jp
CC=golang-dev
https://golang.org/cl/4973045