Makeflow Wrapper: $RULE -> %%

Modified the global makeflow wrapper to use %% instead of $RULE.

Wrapper substitution is neither a macro-expansion at parse-time, nor an environment variable at execute-time.  it needs a different symbol to avoid confusion.  This fixes failing tests in makeflow.

I rather have the function to always return a copy when no changes are made. That way we know it is safe to free the string.