snowball update

[Peter Eisentraut]

There is another snowball release out, and I have prepared a patch to 
integrate it.  It's very big and mostly boring, so I'm not attaching it 
here, but you can see it at

https://github.com/petere/postgresql/commit/d0aa6c2148bcef10942959035ce14f1810873593.patch
Major changes are new stemmers for Armenian, Serbian, and Yiddish.