Tested pgsql driver in production, drop-in replacement for postgres

[Stephen R. van den Berg]

Small heads up for Postgres users:

I've now succesfully compiled pike 7.8 explicitly --without-postgres
yet all existing applications can access Postgres databases just fine
(pgsql automatically takes over the postgres:// url if libpq is excluded
from the build).  I'm running this in a production environment now, no
ill effects so far.

Obviously, pike --features doesn't list Postgres anymore in this case,
but that doesn't mean that it can't access Postgres databases anymore
(is this confusing?).
--
Sincerely,
           Stephen R. van den Berg.
"The state you are in while your HEAD is detached is not recorded by any
 branch (which is natural --- you are not on any branch)." -- man git-checkout

Yes, it's confusing. Please fix.