Use a 32k file buffer on recordings, which increases the efficiency of file recording.

(closes issue #11962)
 Reported by: garlew
 Patches: 
       recording.patch uploaded by garlew (license 376)
       bug-11962.diff uploaded by snuffy (license 35)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@112564 65c4cc65-6c06-0410-ace0-fbb531ad65f3