check for audio capability with modernizr
show proper msg and only when player.paused is false

because player.paused can be undefined for browsers that dont support
audio.

also, chrome and others show return value as a string so set it to a
proper message. firefox just doesnt show the custom message but you
still get the popup
close ws conn on unload and not beforeunload

so the player playing message has a chance to abort it in beforeunload