getting julian number from date in libpq

We're trying to convert dates properly for R.

R stores dates internally as integers, using Unix date style --  
starting date is January 1, 1970.

Postgresql stores dates as Julian days, but using libpq, I don't see  
how to get out a date quickly as a julian day. If I use PQgetvalue,  
my date is automagically converted into whatever my DATESTYLE is at  
the time. How can I just get out the internal julian date? I could  
use this to convert to R dates much easier than using an ISO date  
format.

Thanks for any help.

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