add missing two-weapon feedback

When dual-wielding and you wield a different weapon, two weapon combat
was silently toggled off even when the new weapon was eligible to be
dual-wielded.  If the verbose flag is On, explicitly tell the player
when wielding something toggles off two-weapon mode.  Wielding '-' is
an exception because you already get told that you're empty handed.

doc/fixes37.0

@@ -117,6 +117,7 @@ demon lords hate Demonbane
 pets avoid eating shapeshifter corpses unless starving or nearly feral
 blessed scroll of teleportation gives a single controlled teleport
 allow opening a tin without interruption if slimed
+tell player when wielding a different weapon toggles off dual-wielding
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository