Add GIDs to packages.list, update SD card perms.

Write supplementary GIDs to packages.list for lower-level system
components to parse.

WRITE_EXTERNAL_STORAGE also implies sdcard_r GID. Switch to always
enforce READ_EXTERNAL_STORAGE permission. Update permission docs to
mention new behavior.

Change-Id: I316ba4b21beebb387ac05c80980ae9b38235b37d
diff --git a/services/java/com/android/server/pm/PackageSetting.java b/services/java/com/android/server/pm/PackageSetting.java
index f7f0870..b6f9f5b 100644
--- a/services/java/com/android/server/pm/PackageSetting.java
+++ b/services/java/com/android/server/pm/PackageSetting.java
@@ -52,4 +52,8 @@
             + Integer.toHexString(System.identityHashCode(this))
             + " " + name + "/" + appId + "}";
     }
-}
\ No newline at end of file
+
+    public int[] getGids() {
+        return sharedUser != null ? sharedUser.gids : gids;
+    }
+}