(can_* == can_read, can_write, and can_create) See top of contrib/adc/adc.common-functions for more on this. Note: the old style (calling get_rights_and_owner with $repo, then checking $perm_read, $perm_write, etc.), will still work fine.
set-head was too specific. See comments in symbolic-ref for more on this ADC, but basically it lets you run 'git symbolic-ref' on a repo that you have write access to. (in response to http://comments.gmane.org/gmane.comp.version-control.git/182067)