A build asked at a commit recorded that commit as the module's ref. Every merge after it failed to
match the module and its plan left it out without a word, and every plan that rebuilt it asked for
the same old commit again. Registration now keeps the branch the module followed (the default
branch for a new one); matching and re-asking read a recorded commit as the default branch, which
heals records already pinned this way; and a merge says which modules of its repository it leaves
out because they follow another branch.
jochen
6784efae75