Merge pull request #4006 from RosettaCommons/roccomoretti/tag_self_weak_fix
Remove the string constructor from utility::tag::Tag
It's a nice idea, but unfortunately when read() adds subtags, it uses the shared_from_this functionality.
shared_from_this isn't valid in constructors (or for that matter, anytime the object isn't already in an OP).
The way Tag is structured, you really do need to do a construct-then-read two-step.