config-package-dev: Provide Lintian checks

[geofft]

We should make sure that packages using config-package-dev have

Provides: ${diverted-files}
Conflicts: ${diverted-files}

in their control files. If we implement #1354, we'll also want

Built-Using: ${misc:Built-Using}

These are stanzas in binary packages, and only relevant for those binary packages that involve actually using the config-package-dev tools. I can think of two ways to implement this. One is to check the source packages have the substvars, and perhaps make an effort to avoid false positives if there are things generating multiple binary packages only some of which use config-package-dev. The other is to check that the binary packages do in fact have the correct _values_ in those fields corresponding to what their maintainer scripts divert, although that's harder for the Built-Using case, since transforms and mere displaces are indistinguishable looking at the binary package alone.