Cache sound tarfiles in a common directory, such that a clean reinstall does not force a re-download of the tarballs.

(closes issue #15370)
 Reported by: pprindeville
 Patches: 
       asterisk-trunk-bugid15370.patch uploaded by pprindeville (license 347)
 Tested by: pprindeville, tilghman, seanbright


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@263724 65c4cc65-6c06-0410-ace0-fbb531ad65f3