Cleanup the installation of samples, avoiding repetitions.

I am preserving the behaviour on *.adsi files,
i.e. overwrite anything there without making a backup.
However I am not sure that this is the intended behaviour.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@88675 65c4cc65-6c06-0410-ace0-fbb531ad65f3