BUG #2502: PQclear: "invalid next size"

The following bug has been logged online:

Bug reference:      2502
Logged by:          J. R. Fisher
Email address:      psql@jeffryfisher.net
PostgreSQL version: 8.1
Operating system:   Linux
Description:        PQclear: "invalid next size"
Details:

One patch of C++, two programs using it. One program runs without a hitch,
the other always explodes. In the debugger, this is what's executing:

result = PQexec (conn->handle, cmd);// char* cmd= "BEGIN"
if (PQresultStatus (result) != PGRES_COMMAND_OK) {
    ... // skipped because result *is* OK
}
if (!savingCursor) {
    PQclear (result);    // blows up here, but only in one program, not the
others

*** glibc detected *** free(): invalid next size (normal): 0x08068ab0