Fix git source's shallow history handling with old git
When using an old version of git it will assume that all shallow commits have no parents, and doesn't have
Newer versions of git will accept parents of a shallow commit if it is otherwise included in the history, presumably so that you can exclude only some parents of a commit.
The lack of
--first-parent results in fewer tags being included in the tree, but this is handled without problems for reproducibility, by the tags it actually included being factored into the cache key.
Changes proposed in this merge request:
- Don't treat a tag as a shallow commit if its parents are included.
- Cope with git describe lacking
--first-parentin the test suite.
This merge request, when approved, will close issue/bug: #833 (closed)
- Initial version