contrib uninstall scripts need some love

Awhile back, someone went around and made sure that all the contrib
modules had uninstall scripts, but most of the new contributions since
then don't have 'em:
adminpack hstore pg_freespacemap pgrowlocks sslinfo
all seem to need one. Also, I tested a few of the existing uninstall
scripts in passing while fixing the contains/contained mess, and two
out of four were broken (failed to remove everything installed by the
module, as shown by getting errors if you then try to reinstall it).
Seems like this area needs more attention ... anyone want to work on it?

regards, tom lane