'cabal [install,configure] --constraint' should support constraints on installed package ID

Quoting IRC discussion with @dcoutts:

```
17:46 < refold> dcoutts: should 'cabal configure' accept '--dependency'? It currently does.
17:46 < dcoutts> refold: there's no particular reason why not, unless it doesn't work :-)
17:47 < dcoutts> refold: now that you mention it, it probably just causes problems
17:47 < refold> dcoutts: I haven't tested.
17:47 < dcoutts> given that it'll likely be passed straight through
17:48 < refold> dcoutts: for some reason configureExCommand also has a --constraint option
17:48 < dcoutts> if we wanted that feature in cabal, the better approach would be as a constraint, to pick a particular installed instance
17:48 < refold> which is different from --constraint in configureCommand
17:48 < dcoutts> refold: it accepts a wider range of constraint types
17:48 < dcoutts> like source/installed
17:49 < refold> dcoutts: ah
17:50 < refold> dcoutts: does it support constrains on the package hash?
17:50 < dcoutts> refold: I don't think so
17:50 < dcoutts> but in principle it could
17:50 < dcoutts> that would be reasonable
17:50 < dcoutts> refold: so on that basis, it'd make sense to hide the --dependency flag
17:52 < dcoutts> oh, cabal-install's --constraint also supports flags
17:52 < dcoutts> --constraint='blah +foo -bar'
```

So I'll disable `cabal configure --dependency` for now. We should add support for constraints on specific installed package instance if we want to make this feature available via `cabal configure`.