[CMake] QT4_CREATE_TRANSLATION delete source ts files during clean

[Stephen Kelly]

Anatoly Shirokov wrote:

> Guys!
> 
> I have fixed bug related to delete translation (ts) file during clean
> (someone meet the same problem here
> http://cmake.3232098.n2.nabble.com/How-to-not-delete-generated-files-on-make-clean-td4425991.html)

I agree with the point that Hendrik Sattler makes that it is better to 
separate the process of translation from the build process.

I think it's fairly reasonable for 'make clean' to remove buildsystem 
artifacts. You should be able to rm your build dir at any time without 
losing work. If you do in-source builds, you shouldn't :).

Alex, Clinton, any comment?

Thanks,

Steve.