Invert logic for the last commit

This makes it more clear that the option is meant to be a special
case (it *disables* part of the focus handling). Also, when
initializing the config data structure with zeros, it will get
initialized with the right value.

Furthermore, the config file parser now also accepts various values
which represent "true", not only numbers.

src/cfgparse.y

@@ -381,10 +381,27 @@ new_window:
         }
         ;
 
-focus_follows_mouse:
-        TOKFOCUSFOLLOWSMOUSE WHITESPACE NUMBER
+bool:
+        NUMBER
         {
-                config.focus_follows_mouse = ($<number>3 == 0 ? 0 : 1);
+                $<number>$ = ($<number>1 == 1);
+        }
+        | WORD
+        {
+                DLOG("checking word \"%s\"\n", $<string>1);
+                $<number>$ = (strcasecmp($<string>1, "yes") == 0 ||
+                              strcasecmp($<string>1, "true") == 0 ||
+                              strcasecmp($<string>1, "on") == 0 ||
+                              strcasecmp($<string>1, "enable") == 0 ||
+                              strcasecmp($<string>1, "active") == 0);
+        }
+        ;
+
+focus_follows_mouse:
+        TOKFOCUSFOLLOWSMOUSE WHITESPACE bool
+        {
+                DLOG("focus follows mouse = %d\n", $<number>3);
+                config.disable_focus_follows_mouse = !($<number>3);
         }
         ;