Strife: add demo fast forward functionality (#1367)

.. based upon doom implementation.

Author: Noseey

src/strife/g_game.c

@@ -1082,6 +1082,14 @@ static void SetMouseButtons(unsigned int buttons_mask)
 // 
 boolean G_Responder (event_t* ev) 
 { 
+    // [crispy] demo fast-forward
+    if (ev->type == ev_keydown && ev->data1 == key_demospeed && 
+        (demoplayback || gamestate == GS_DEMOSCREEN))
+    {
+        singletics = !singletics;
+        return true;
+    }
+
     // allow spy mode changes even during the demo
     if (gamestate == GS_LEVEL && ev->type == ev_keydown 
         && ev->data1 == key_spy && (singledemo || !gameskill) ) // [STRIFE]: o_O
@@ -2313,6 +2321,8 @@ void G_DoNewGame (void)
     netdemo = false;
     netgame = false;
     deathmatch = false;
+    // [crispy] reset game speed after demo fast-forward
+    singletics = false;
     playeringame[1] = playeringame[2] = playeringame[3] = 0;
     respawnparm = false;
     fastparm = false;