Debugger doesn't allow setting environment variables for the target application

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Though perhaps it wasn't common in the Visual C++ 6.0 era, most modern debuggers allow setting environment variables for the target process when it is debugged. This feature is unfortunately missing in the Dylan command-line and GUI environments (which is especially inconvenient when debugging the environment with itself), and is not present in the underlying run-application interface (from environment-protocols). A feature for setting application environment variables should be added.