SOUND_CACHE_DIR now defaults to empty

SOUND_CACHE_DIR now defaults to empty

Sounds files included in the Asterisk tarball were being ignored and
re-downloaded.  Users wanting to cache the files can still override the setting
using the --with-sounds-cache option.

(closes issue #18589)
Reported by: pabelanger
Patches:
      issue18589.patch uploaded by pabelanger (license 224)
      Tested by: pabelanger

Review: https://reviewboard.asterisk.org/r/1074/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.6.2@301220 65c4cc65-6c06-0410-ace0-fbb531ad65f3