Change command X to twoweapon toggle

Explore mode is now an extended command #exploremode.
There's no sense that a command used max. once per game, and
in normal games not at all, takes up a key. So, analogous to
the 'x' command (swap weapons), 'X' now toggles two-weapon
combat.

dat/cmdhelp

@@ -69,7 +69,7 @@ V       Show long version and game history
 w       Wield (put in use) a weapon
 W       Wear a piece of armor
 x       Swap wielded and secondary weapons
-X       Enter explore (discovery) mode (only if defined)
+X       Toggle two-weapon combat
 y       Go northwest 1 space
 Y       Go northwest until you are on top of something
 ^Y      Go northwest until you are near something

dat/help

@@ -147,7 +147,7 @@ Commands:
         w       Wield weapon.  w- means wield nothing, use bare hands.
         W       Wear armor.
         x       Swap wielded and secondary weapons.
-        X       Switch the game to explore (discovery) mode.
+        X       Toggle two-weapon combat.
         ^X      Show your attributes.
         z       Zap a wand.  (Use y instead of z if number_pad is -1.)
         Z       Cast a spell.  (Use Y instead of Z if number_pad is -1.)

dat/hh

@@ -32,7 +32,6 @@ O       options set options
 \       known   display list of what's been discovered
 v       version display version number
 V       history display game history
-X       explore switch the game to explore (discovery) mode
 ^A      again   redo the previous command (^A denotes the keystroke CTRL-A)
 ^R      redraw  redraw the screen
 ^P      prevmsg repeat previous message (subsequent ^P's repeat earlier ones)
@@ -70,6 +69,7 @@ T       takeoff take off some armor
 w       wield   wield a weapon  (w-  wield nothing)
 W       wear    put on some armor
 x       xchange swap wielded and secondary weapons
+X       twoweapon toggle two-weapon combat
 z       zap     zap a wand  (use y instead of z if number_pad is -1)
 Z       Zap     cast a spell  (use Y instead of Z if number_pad is -1)
 <       up      go up the stairs