Description of problem:
dnf silently hides repo dependency breakage.
While this may generally enhance the UX,
it is sometimes desirely to know about broken
dependencies for "dnf update", etc.

So I would suggest adding an option "--show-broken-deps"
(probably not the right name;) that would should
ENVRs that dnf is excluding from a transaction.

Currently I use yum-deprecated for this,
but this is inefficient.