Fix git clone & update helper scripts

[remram44]

Creating local branches is a bit weird, and moving them is definitely not a good idea.

This places Git in "detached head" mode without creating or changing local branches. Remember that BRANCH might very well be a tag name.

[remram44]

Note that the local branch refs/heads/@BRANCH@ will still be created with upstream information (but not checked out); this is because of clone -b.

[aashish24]

So the logic is:

1. if tag then create the branch?
2. if not create the headless branch?

[remram44]

1. If tag then no branch is created. Goes to detached head, like it already does, except that the update script will work too.
2. If branchname then a local branch is created by "git clone". I guess I could just run branch -D to get rid of it. Goes to detached head, the update script will work (and won't create local branches).

[aashish24]

Right..
For the 1) I was misled by my prompt that I have a branch checked out. In both cases it will be detached head.

[aashish24]

LGTM 👍

[remram44]

Interesting detail: this will fail if someone was to make a lightweight (old-style) tag instead of the new, preferred annotated tags (git tag -a). Apparently came up today with VisTrails' tag for uvcdat-2.2.0.