For this to apply to your ~/common-lisp/ you'd have to list ~/common-lisp/ explicitly, and then :ignore-inherited-configuration to avoid the regular entry for ~/common-lisp/ and then explicitly include any configuration you'd like to inherit anyway.
ouch.
is there any other way to tell :tree to ignore some branches?
it would be useful both for optimization, and also for dealing with different versions of the same system. in my original config my hand-written scanner was e.g. ignoring _foo directories, so i could just rename dirs to use a different version.
i'd like to use a default config with as little interference as possible, so i don't want to just shadow all the /etc/common-lisp/... configs.