contrib: Fix installation of kashmir-dependency, other fixes.

* contrib/src/main.mak (dep_on): Filter out top-level packages
from the result (as it used to be prior to commit 6fa37b57).
(pprint): Display 'None' when there are no packages selected.
* contrib/src/kashmir-dependency/rules.mak (.kashmir-dependency):
Ensure installation directory exists before copying files.
* contrib/src/asio/rules.mak: Do not add to PKGS. This prevent build
this indirect dependency when its parent referrer was disabled.
* contrib/src/kashmir-dependency/rules.mak: Likewise.
* contrib/src/restbed/rules.mak: Likewise.

Change-Id: I58e515c4e4e49220f0e82144b349c97ba86d6940
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>