A broken transitive dependency reports failure on the parent bit

When a bit depends on another bit that is broken, `cpm` shows an invalid error message:

```
$ cpm install chromos-channels
installing chromos-channels:latest
installing zeromq:4.3.2
CPM: error: bit chromos-channels not found in CPM Hub
```

In this case, it was `zeromq` the bit that wasn't found:

```
2020-06-20 11:24:20.640 info - 127.0.0.1 - - [20/Jun/2020:11:24:20 +0200] "GET /bits/chromos-channels HTTP/1.1" 200 8826
2020-06-20 11:24:20.655 info - 127.0.0.1 - - [20/Jun/2020:11:24:20 +0200] "GET /bits/zeromq/4.3.2 HTTP/1.1" 404 0
```

Reproduce the failure with `cpm install chromos-channels` and inspect how dependency-install errors are reported. Confirm that the message identifies `zeromq` rather than the parent bit `chromos-channels`; no specific source file or test is named in the issue.

Written by the indexing model from the issue text.