Stefan, Juri, here's a new version of the patch for filtering packages
by name.

Because I added the new function `package-menu-clear-filter' (bound to
'/ /'), I decided to remove the behavior in `package-menu--generate'
that previously bound 'q' to clearing the filter. I think it's better
the way it is now because the user can now bind
`package-menu-clear-filter' to whatever they like.

Thanks!

- Federico