REBASE add basic VerifyActivity to check .sig files
REBASE add DecryptActivity to handle decrypting anything we throw at it
EncryptFileActivity some misrouted Intents might have null extras
kludge to prevent FC when an Exception happens in onPostExecute()

This should be handled better, probably. It seems like this happens when
the Activity starts then stops to quickly, usually due to a problem with
the Activity that is supposed to handle the ACTION_VIEW after the crypto
action is complete.  This stuff should be replaced by a real Service with
a Notification.

refs #1482
handle .key file type as application/pgp-keys

On Samsung Galaxy Player 5.0 running Android 2.3.6, it converted a .pkr
file to a .key file, and labeled it 'application/pgp-keys'. This happened
in the Gmail app, but Astro File Manager did not know about the .key file,
so we need to manually claim .key like the other extensions.

refs #1455 refs #1456