MediaStore.Audio.Media.getContentUriForPath() returns unexpected content

MediaStore.Audio.getContentUriForPath() returns an uri to
internal storage if anything but /mnt/sdcard/ is sent in.
This fix checks if there is an additional sdcard
(normally called ext_card) or usb mass storage attached to
the device and then returns an uri to the external db.
The extra sdcard name and the usb mass storage name info is read from
the system environment variable SECONDARY_STORAGE so if a customer
chooses to change the name this will work as expected.

Change-Id: Ib78bca929fe382d4770df895149a0132f0e56994
Process all display events in order

Display events in each batch received from IPC were being processed in
reverse order, and stopped after the first vsync event (latest
chronologically) was handled. This makes perfect sense for vsync
events, but is broken for hotplug events.

Now we process them all in order, handling all except vsync as we see
them. For vsync events, only the last is reported.

Bug: 7491120
Change-Id: I448d139d21dc27128d75ca1d661de666fff51bcb