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

[Michael Scott]

> Most of that change appears to be just the number of spaces after a
> period.  I prefer two which is why the original message was that way.
Ah fair enough, I assumed the two spaces was a typo and was meant to be 
just one space.  Yes essentially the third patch just replaces the two 
spaces with one, so it can be just ignored in this case.

> IIRC we previously concluded that the individual callers don't have to
> deal with the message type change so long as the overall process exits
> with an error.  Is this currently achieved by the patch?
Yes that will now happen with the patch, the cmake::displayMessage 
method will set the error occurred flag, though not the fatal flag, when 
a deprecation or author error message is displayed. In this case I think 
there are no issues I'm aware of with the proposed changes.

If there are any problems with the proposed changes let me know.

Cheers,
Michael