REBASE PrivateFilesProvider: add debugging logging for the unsupported methods
EncryptFileIntent: handle encrypting random files coming from SEND Intents

* This also adds the logic to finish() this Activity once the receiver is
  finished with it.  If its a file in the private files stash, then it'll
  delete them when the process is done, since these are tmp files.

* The resulting encrypted file is shared using a file:/// URI because most
  of the apps that will receive this only seem to work if its a file:// URI
  and not if its a content:// backed by a stream (Dropbox, Gmail, K-9...)

closes #1454