Will libpq 8 PQ*cancel functions work with 7.4 servers?

Ave!

I'm porting an X application using asynchronous libpq calls from libpq
version 7.4 to version 8.0. One of the things I have to change is the
way of cancelling the queries (the old way, using PQrequestCancel, is
marked as deprecated).

My question is, will the new interface (PQgetCancel / PQcancel /
PQfreeCancel) work with the version 7.4 server? I'd rather not migrate
the server to 8.0 right now, it's a long and painful process (the
database holds about 14 millions tuples).

Also, is there a list of libpq changes between 7.4 and 8.0 available
anywhere?

Regards,

Piotr Sulecki.