Improve pg_dump dumping publication tables

Hi hackers,

I was wondering if there's a good reason in pg_dump getPublicationTables() 
to iterate through all tables one by one and querying to see if it has a 
corresponding publication other than memory concerns?

Attached is a patch to construct the publications by querying for all publications 
at once and then finding the corresponding tableInfo information in tblinfoindex. 

It seems more likely that users will have a lot more tables than publications so 
this should be a lot faster, especially when there's millions of tables.

Setup: 
time pg_dump --schema-only -d postgres -f dump.sql -v 2> dump.log
10k tables, each table having its own publication.

Before patch:
real    0m6.409s
user    0m0.234s
sys    0m0.584s

With patch:
real    0m5.483s
user    0m0.399s
sys    0m0.443s

10k tables, no publications.

Before patch:
real    0m6.193s
user    0m0.276s
sys    0m0.531s

With patch:
real    0m5.261s
user    0m0.254s
sys    0m0.377s

Thanks,

John H