se: No driver installation prompt

Tested with vbox 3.1.2 and rev 46702 and 46732 with the same result:
AC97 installs and gets listed under device manager but you can't play anything, winamp says unsupported PCM Format, and "Sound", "Audio" and "Voices" are greyed out in control panel under properties for sound and audio devices.

Appears as: (ntoskrnl\se\semgr.c:705) HACK: Should deny access for caller: granted 0x0, desired 0x100000 (generic mapping B1284ED8).