Vendoring in Go 1.6 breaks gob registration

[jcooklin]

When using vendoring in Go 1.6, reflection is in gob.Register to create
a key for type lookups. This reflect.PkgPath() call returns a "globally
unique" key for looking up types, and in the case of a vendored type, is
not valid for matching gob registration names. This is because on the
server side, the type is registered as import/path.(typename), but on
the client side (vendored) it looks like
client/vendor/import/path.(typename). Using fixed keys bypasses the
need for reflection and is safe on either side, even when using
vendoring.