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By contrast with `INSTRES_FILES` in `CModule`, where `Messages` is implicitly
included, `CApp` and `BasicApp` do not do this for `RES_FILES`. The native-
compilation version of `CApp` was doing duplicate installations of `Messages`,
which was at odds with the cross-compiling `CApp` and both versions of
`BasicApp`. If this version of `CApp` is used with a component that doesn't
feature a `Messages` file (such as the in-development `InetRes`) this results
in an error.

The only existing `CApp` client components that define `RES_FILES` are
`Help2` and `EditApp`, and they both explicitly list `Messages`, so this
change should not break either of them.