It's not clear to me in what version of PostgreSQL the pgxs system was
introduced.  I *thought* it was 7.4, but I'm only seeing it clearly
described in the docs
(http://www.postgresql.org/docs/[version]/static/xfunc-c.html) as of
version 8.0.

One of the "to dos" is to use pgxs; if it is not supported by 7.4, which
we *do* need to support, then it seems to me we need to put off pgxs
usage until such time as we have decided to eliminate support for 7.4,
which probably won't be for a while...

Does any of that look blatantly wrong?  Let me know...