Prompts based on `mkComplFunList` and `mkComplFunList'` were not
taking into account the `searchPredicate` funtion from `XPConfig`.
This was rather confusing.
We fix it by passing `XPConfig` to these functions; although
this is strictly more than they need, it makes the breaking change very
easy to fix and is also more future-proof.
The latter is pretty useless, as there's no way to find out what
layouts are available, but it can at least allow you to select between
any layouts that you happen to be using already (in one workspace or
another). The former is handy any time you'd rather have a short name
for a layout (either for selecting, or for viewing in a status bar).
