Reimplement what cargo does to detect bad renames

[sayrer]

As surfaced in #282.

The problem manifests from this:

[dependencies]
bytes_new = { version = "0.3.0", package = "bytes" }
bytes_old = { version = "0.3.0", package = "bytes" }

Strictly this is an error. Right now cargo metadata will basically lose both bytes deps
from the resolve graph, but a cargo build will scream about having the same basic
package with multiple names.

Currently there is no good solution using metadata.