Fix tag detection for git clone/update scripts

[remram44]

Amends #993

Checking that the object type is "tag" only works for annotated tags. If case someone decides to make a lightweight tag (or does it by mistake), it will now correctly be handled.

Interestingly, this only seems to be used by 'vistrails', so I don't think it will fix build warnings like:

[INFO] [PIP] Installing UVCMETRICS from GIT_REPOSITORY;git://github.com/UV-CDAT/uvcmetrics.git
fatal: ambiguous argument 'origin/uvcdat-2.2.0': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

which I think just leak through from ExternalProject but are not actual errors(?)

[aashish24]

I thought the problem would be here with -b option since that would not respect light weight tags.

[remram44]

-b works with lightweight tags as far as I can tell

[aashish24]

On certain git versions it does not (you should see reporting on this if you do a google search). I would suggest, we take out the -b option, and just checkout the right branch / tag afterwards.

[remram44]

Will do

[remram44]

It looks like --depth cannot be used if we get rid of -b, else git only gets HEAD and the ref we need might not be fetched at all.

[aashish24]

In that case, merging this one. We will deal with this issue later then.