[CMake] Embedding up-to-date version info in built library

[Kolja Waschk]

Hi, thanks,

> One question: Why do you need a add_custom_command with all those
> dependencies? Why does version.cc depend on all the source and header
> files? What do you write in your version.cc file? Is it something like

Beside the SVN revision number of the working base, our embedded
revision information also tells whether the library was built from code
with local modifications, i.e. whether it equals the source code stored
in the SVN repository or was changed afterwards.  Changing a single byte
in a header file already affects that state, so all headers need to be
watched.

Kolja