some more pg_dump refactoring

Here is a patch to reorganize dumpFunc() and dumpAgg() in pg_dump, 
similar to daa9fe8a5264a3f192efa5ddee8fb011ad9da365.  Instead of 
repeating the almost same large query in each version branch, use one
query and add a few columns to the SELECT list depending on the
version.  This saves a lot of duplication.

I have tested this with various old versions of PostgreSQL I had 
available, but a bit more random testing with old versions would be welcome.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services