Fix switching running/cached apps with memory bar

Fixes upstream issue #38735
http://code.google.com/p/android/issues/detail?id=38735

Ported from CM10
http://review.cyanogenmod.org/25775

This patch is already submitted to AOSP. No feedback from them yet.
https://android-review.googlesource.com/45993

Change-Id: I484e30d3fd4f5425e174911ae22bb2def170e6b8
Show memory full text only for internal storage

When the internal memory is full, a warning text is shown
in Settings/Storage. This warning was displayed for all
types of memory (internal/primary, sd card and usb storage)
even though it was only referring to the primary memory.
With this fix, it is only shown for the primary memory.

Change-Id: I35ad4b0b45c6752ddc9d7166495435b27fd4a170