Weird ecpg failures on buildfarm NetBSD members

Today's puzzler for the curious:

Last night the buildfarm reported two ECPG-Check failures

http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=salamander&dt=2007-07-08%2017:30:00
http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=canary&dt=2007-07-08%2017:30:01

which promptly went away again.  Judging by the timestamps these must
have been induced by Joe's PQconnectionUsedPassword() patch and fixed by
my subsequent tweaking, but how the heck did that result in an ecpg
failure?  I think that the cause must have had something to do with his
inclusion of postgres_fe.h into libpq-fe.h, which I took out on the
grounds that it was an unacceptable pollution of client code namespace.
But exactly why/how did that break ecpg, and why did the failure only
manifest on NetBSD machines?

I don't really have time to investigate this, but would like to know
what happened.
        regards, tom lane