tab completion of IMPORT FOREIGN SCHEMA

I use IMPORT FOREIGN SCHEMA a bit to set up systems for testing. But not
enough that I can ever remember whether INTO or FROM SERVER comes first in
the syntax.

Here is an improvement to the tab completion, so I don't have to keep
looking it up in the docs.

It accidentally (even before this patch) completes "IMPORT FOREIGN SCHEMA"
with a list of local schemas. This is probably wrong, but I find this
convenient as I often do this in a loop-back setup where the list of
foreign schema would be the same as the local ones. So I don't countermand
that behavior here.

Cheers,

Jeff