I'm reworking QueryExecutor/ProcotolConnection implementation as a part of "smarter returning" (https://github.com/pgjdbc/pgjdbc/issues/488), and I would like to just drop v2 support.
As far as I know, v3 was introduced in PostgreSQL 7.4, thus it looks rather safe to just drop v2 support in pjgdbc.
By the way, the oldest version we test in Travis is 8.4