I had to make two minor fixes while migrating my work repos:
1. I forgot to honor '@all'; oops!
While I was about it, I also fixed the "access denied"
message to show what rights were being tried when it
failed.
2. I forgot that URLs can have leading slashes (I myself
only use URLs like gs:reponame.git, where gs is an ssh
stanza that describes the git server in question).
Ilari pointed out that in case of branch deletion the *new* SHA could be 0,
which causes an ugly
fatal: Not a valid commit name 0000000000000000000000000000000000000000
Since we consider deletion an extreme form of rewind, the end result does not
change ($merge_base will be unequal to $oldsha anyway), but we do need to
squelch the ugly message.
