amavis not properly sending mail to spamassassin

[Christopher Engelhard]

Found the problem - as usual, PEBKAC: I had a typo in $sa_configpath, so
SA when called from Amavis never loaded it's default config, only my
overrides. So of course all my individual config was working, but
nothing else ...

For future reference: SA failing to read it's default configuration
(typically /usr/share/spamassassin or similar, not /etc/...) is not
reflected in its log output, just causes weird errors.