contacts: Privacy Guard support

 * If privacy guard is enabled for the calling process, return an empty
   MemoryCursor (with column names populated) instead of the real dataset.

Change-Id: I78b16f3791706636d51785e46a1f2ec656a3c9d2
Merge branch 'cm-10.1' of https://github.com/CyanogenMod/android_packages_providers_ContactsProvider into DJL10.1