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.
- factored out all the pathnames etc to an rc
- taught it to create repos that dont exist but are mentioned
- promoted user up one level (moving ref down) because gl-auth needs it
- REPO_BASE no longer contains $HOME so that has to be added in manually
- little bugs here and there, like in @refs
