[Bug: 21.5-b29] packages UI: non-ideal handling of missing deps

[Stephen J. Turnbull]

Samuel Bronson writes:

 > Oh. Those are autogenerated compile-time dependencies?

Unfortunately, they're not even autogenerated for compile time.

 > Maybe the UI help should make that a bit clearer.

Patches are welcome.  The issue is now in the tracker, so somebody
should get to it eventually, but as I mentioned before, core people
aren't likely to get to it for a while.