[Cmake] SOURCE_FILES default extension

[Ken Martin]

I think we should start using extensions in all our cmakelist files.
But for backwards compatibility I don't think we can disallow people
from not having the extension. We can

1) add a check so that if the extension was not provided and we find
multiple versions of a file we print a warning

2) when multiple matches are found favor foo.cxx foo.c foo.h over
plain foo.

In general I'm trying to be more careful that new cmakelist files will
work with old versions of cmake (or at least provide a message
indicating what version someone needs) and that old cmakelist files
will work with new version of cmake.

Ken


> I agree with Bill L: I think it should be mandatory to put
> an extension
> on the file name.  Can't we provide a script which will fix the
> cmakelists and give a warning for a short while before breaking
> projects?  As with VXL, there are inevitably going to be
> times when you
> need to break things for the sake of sanity, and I think this is an
> example.