Simplify usage of Replaces

This draft is intended to fix a long standing paper-cut where any use of "Replaces" always requires at least one other field. Notably the trivial case of wanting to move a file between two packages requires:

Breaks: foo (<< 1.0~)
Replaces: foo (<< 1.0~)

Proposal

It should not require specifying the same value in 2-3 fields to get what you want. Especially, when the absence of these "unrelated" fields have non-obvious effects.

Current usages of Replaces: