Add required database and origin filtering for logical messages.

Logical messages, added in 3fe3511d, during decoding failed to filter
messages emitted in other databases and messages emitted "under" a
replication origin the output plugin isn't interested in.

Add tests to verify that both types of filtering actually work. While
touching message.sql remove hunk obsoleted by d25379eb.

Bump XLOG_PAGE_MAGIC because xl_logical_message changed and because
3fe3511d had omitted doing so. 3fe3511d additionally didn't bump
catversion, but 7a542700 has done so since.

Author: Petr Jelinek
Reported-By: Andres Freund
Discussion: 20160406142513.wotqy3ba3kanr423@alap3.anarazel.de