fc4e8da727
To improve performance on fork+exec impoverished systems (such as Windows) we want to avoid running git-symbolic-ref on every rescan if we can do so. A quick way to implement such an avoidance is to just read the HEAD ref ourselves; we'll either see it as a symref (starts with "ref: ") or we'll see it as a detached head (40 hex digits). In either case we can treat that as our current branch. Signed-off-by: Shawn O. Pearce <spearce@spearce.org>