[CMake] documentation for important cmake variables

[Brad King]

Alexander Neundorf wrote:
> the cmake man page doesn't document important variables like e.g. 
> CMAKE_SOURCE_DIR. Is there another place where they are documented ? If 
> not, would you mind if I add a page to the cmake wiki ? (do I need a 
> login or something to do this ?) 

The man pages are generated by the cmake executable so that the 
per-command documentation always remains up-to-date.  At the time the 
generation code was written there were not very many "special" 
variables.  Currently the only place I know the variables are documented 
is in the "Mastering CMake" book.

If you want to add a page to the Wiki that would be fine.  Eventually we 
would like to have the documentation generated like the current command 
documentation, but until someone has time to do this the Wiki will be a 
good place.

-Brad