Improve doc on built-in application selection

Add examples for `mode=fcm_make` and `mode=rose_prune`.
Raise exception on incorrect application mode.
Merge branch 'master' into rose-app-run-mode-err
Merge branch 'master' into rose-app-run-mode-err
Merge pull request #813 from matthewrmshin/rose-app-run-mode-err

rose app-run: Improve doc on built-in application selection
Merge branch 'master' into t-rosie-ws-braces