git-codereview: add branchpoint command, for scripts

The most important use of this is

	git rebase -i $(git codereview branchpoint)

in multichange clients.

Change-Id: I6bdbc02db2e2823e837159efec20ad5c9046bcd5
Reviewed-on: https://go-review.googlesource.com/2783
Reviewed-by: Andrew Gerrand <adg@golang.org>
5 files changed
tree: c73344b02d89648e0bc5685c35b817b715bbf677
  1. .gitattributes
  2. README
  3. git-codereview/