DO NOT MERGE: Cherry-pick 2ed52496 to JB.

This was contributed from AOSP, a fix to the management of URI write
permissions.  This is a very blatant bug, and with the new Intent ClipData
and other stuff we are making much more use of write permissions in JB,
so it is well worth taking.

Change-Id: I58c86119b4d5c13fefd090944bea139803df1a48