libwnck3: fix build via disabling introspection

It isn't used anywhere, but fixing it won't hurt (I found by accident).
shared_mime_info: update 1.1 -> 1.2
libnotify: minor update 0.7.5 -> .6
libatasmart: update 0.17 -> 0.19

Alas, no NEWS anywhere.
From skimming git shortlog I see nothing special -- hopefully OK.
libcroco: minor update 0.6.6 -> .8
librsvg: comment on why the version isn't updated
xfce4notifyd: minor update, add to the default installation