be rebuilt in the install stage if variables were overridden. This resulted in the finished binary trying to load /usr/local/share/examples/mutt/Muttrc rather than /etc/mutt/Muttrc, most visible by a change in 'header weeding' for people who didn't have ignore/unignore set in their own config, reported by Anthony Campbell and tb@. Tidy up some patch/subst mess while there.