parse_pgarray: allow None
londiste add: --skip-non-existing option
grantfu: 2-pass processing

First revokes, then grants.

This supports one-object-in-several-sections situation.

Although that is bad style and better avoided, current
behavour results in unobvious breakage.
londiste status: make node name easier to select
londiste copy: fix data filtering when parallel_copies > 1

The problem appears in 'catching-up' phase were code checked
table status only and not whether the table is owned by
current process.  Then events can be replayed by several copy
processes when they are all in catching-up phase.

The problem does not appear when local_only=1.

Also remove unused function.