[CMake] File modification detection based on content (not timestamp)

[Robin Vobruba]

Hello everyone!
If you are busy, just read the QUESTIONS part below, plus SIDE-NOTE

I am a dev of the spring game-engine open-source project. We are
gradually moving from SCons to CMake, mainly because of the speed gain
when compiling and better multi-platform support.

We also recently moved from SVN to GIT with our main repository.
Because of the way GIT works, we would like CMake to check for file
modification based on file contents, rather then timestamps. This
would let us use the advantages of GIT to its fullest, save us from
keeping a separate local repository for each branch, and in general
make development much more comfortable.
If you want me to further explain all this, i would be happy to do that.

After browsing the web, the CMake site and the mail archive forum, i
could not find more information then this:
CMake relies solely on timestamps for checking file modification.

### QUESTIONS ###
1. Is file modification detection based on file content instead of
timestamp supported already?
2. Is support for it planned?
If not, i would like to make a feature request!
3. How hard would it be to implement that?

### SIDE-NOTE ###
if possible, could you add a link on the mail archive page to "search
this page with google" or something like this? i did it manually (eg:
"timestamp site:http://www.cmake.org/pipermail/cmake/"), and it works
very well.
searching posts through clicking through all the months is
uncomfortable, and i guess many skip it and rather double post
therefore.