[cmake-developers] Review request: extract-cmMessenger branch

[Michael Scott]

> * Decrease responsibilities of the cmake class. CMake uses too few
> classes for too many things
I certainly agree with that, the cmake class is very large at this point.

> * Make it possible to make add first-class handling of messages about
> missing packages (for example) to cmake-gui by making methods on
> cmMessenger virtual and subclassing
This sounds like a good idea and makes a lot of sense.

While working on the message functionality previously it felt like it 
was tacked on as an afterthought, I think moving in this direction will 
help lead to message functionality that can be expanded and improved 
upon much more easily in the future.

This may be a stupid question, but I previously wondered why CMake 
doesn't use (or at least obviously use) a standard logging library, 
similar to log4j, for some of this stuff?

Cheers,
Michael