xsession: Install session support files after kdesrc-build run.
Currently we install after printing out the various failure category results. There is a "--delete-my-settings" option that is mentioned to override the file collision detection, but it's not actually implemented. We do automatically ignore file collisions if the previous version was installed by kdesrc-build, we use md5 digests to detect this case. I will still need to rearrange the variables so that *only* kdesrc-build-controlled changes are made in kde-env-master. E.g. KDEHOME might be changed by the user... but then kdesrc-build will always complain that it wants to overwrite it. We're getting close though. :)