Makes pg_dump sort overloaded functions in deterministic order.
The field "proiargs" has been added to FuncInfo and is set by getFuncs()
and getAggregates() for all functions and aggregates.
DOTypeNameCompare uses this field to break ties if the name and number of
arguments are the same. This avoid having to default to OID sorting.
This patch is independent from the ongoing discussion of the pg_dump --split
option. Even if we can't agree on how to do the splitting of objects into
files, it still makes sense to fix the sort order of overloaded functions.