[CMake] Regenerating project files based on external file.

[The Novice Coder]

The short version of what I'm trying to do:
Add some kind of definition to the cmake file that specifies a file, 
that if modified, will cause the project to be regenerated.


Longer (more specific) version.
We (our small program team) want's to use cmake to generate a file 
"svn_version.h", which has a solution posted on the web.  The problem 
happens when we checkout new revisions, this file goes unmodified.  
Looking for a way to cause CMake to regenerate the build files (and with 
it, the revision number) after an "svn up" command, without having to 
touch cmakelists.txt.  It would be trivial to simply check files in the 
.svn folder for modification times, so that would probably be the 
easiest (although not 100% accurate) way to go.

Any help on where to look... Thanks!