[cmake-developers] Add command line options for deprecation message control

[Michael Scott]

> I'm going to proceed with my reversion of the entire feature for 3.4.
> We can pick this up during post-3.4 development when you have time.
> Then we can review the all related semantics together.

Okay, that's fair enough, sorry it hasn't been possible to get it into 
the 3.4 release in time.

Cheers,
Michael