Dereference commits in the tag list class, not the load strategy. Fixes #12

Dereferencing commits in the tag list load strategy is too early. In particular, tags that point to other tags need to reference back into the tag list to get the tag object they point to.  When triggering this from the strategy, the tag list hasn’t actually been fully loaded yet, so the tagged tag lookup fails.
Merge branch 'master' of github.com:xiphux/gitphp