structs from libpq-fe.h, as we previously discussed.

There turned out to be sloppy coding practices in more places than
I had realized :-(, but all in all I think it was a well-worth-while
exercise.

I ended up adding several routines to libpq's API in order to respond
to application requirements that were exposed by this work.  I owe the
docs crew updates for libpq.sgml to describe these changes.  I'm way too
tired to work on the docs tonight, however.

This is the last major change I intend to submit for 6.4.  I do want
to see if I can make libpgtcl work with Tcl 8.0 before we go final,
but hopefully that will be a minor bug fix.