Fixes Issue 1448

Fixes ClassCastException.

Also:
Envelope and star in Accounts Activity are now both "hot".  Tapping
the main part of the search opens the full search; tapping the
envelope opens the search only for unread messages; tapping the star
opens the search but only for starred messages.

The envelope and star are a bit small to reliably tap.  Both options
should be available via long-press, also.

Methodology will be extended to real accounts, as well.