As of today there are two new functions exported by libpq.so since
8.2 (lo_truncate and PQconnectionUsedPassword). Currently,
libpq/Makefile sets the major.minor shlib version to 5.1 as compared
to 5.0 in PG 8.2. Should it be 6.0? I seem to recall people
chastizing us for not bumping the major version if there were any
ABI changes at all, forward-compatible or not.
regards, tom lane