Bug 1061702: Stop audio sources from continuing to play garbage after being stopped r=roc a=lmandel
 * clear audio callback buffer if no streams have audio
Revert changesets d04d205b6c1 and b4e9b4dab577 because they landed with the wrong bug number.
Bug 1093316 part 1: Backout changeset aece7f9f944c (i.e. backout bug 1032922 part 2). a=lmandel
Bug 1093316 part 2: Backout changeset af2a4fb980ad (i.e. backout bug 1032922 part 1). a=lmandel
DONTBUILD because just re-landing to fix bug number