libpq api wart: no PQconnect variant that can consume output of PQconninfoParse(...)

Hi all

While working on something else I just noticed that there's no PQconnect
variant that can consume the output from PQconninfoParse(...), i.e. an
array of PQconninfoOption* .

This would be a nice-to-have for times when you want to pass a connstr,
modify it, and then connect with the modified options.

There's PQconnectdbParams, but you have to transform the option arrays
to use them with it.

This might be a worthwhile TODO (beginner) option - and may simplify
some of fe-connect.c in the process.

-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services