#46 Avoiding configuration leaks

[Nick Vlad]

The current configuration system suffers from the weakness that even if the need for a certain special dependency is eliminated in the codebase, the configuration check for that dependency remains, because nobody knows if that dependency is needed elsewhere or not. Madagascar installation may fail because of an unneeded exotic dependency! There should be a system of tags defining dependencies, and the SConstruct in each directory should specify which of these dependencies are needed. The configuration step should recursively walk the directory structure and only execute config checks for those components that are needed. Such a system would also identify which and how many Madagascar artifacts use each dependency, helping with decisions about whether to include third-party code or to rely on the dependency being present.