am 407f625a: Add new API to find out whether external storage is removable.

Merge commit '407f625a9b8e356e765a5ec587c443af1f3aadb5' into gingerbread-plus-aosp

* commit '407f625a9b8e356e765a5ec587c443af1f3aadb5':
  Add new API to find out whether external storage is removable.