force camino to tab to form controls, regardless of the system pref. this

best matches user expectation as nobody knows about the system pref, or that
that particular pref would impact camino's content area tabbing.

camino/resources/application/all-camino.js

@@ -38,6 +38,8 @@
 
 // This file contains Camino-specific default preferences.
 
+pref("accessibility.tabfocus", 3);
+
 // What to load in a new tab: 0 = blank, 1 = homepage, 2 = last page
 pref("browser.tabs.startPage", 0);