Use "on"/"off" when displaying bool parameters

This is a lot more readable than "0"/"1", which can easily be confused
with integer parameters.

Note that this breaks some backwards compatibility. Older clients will
not be able to parse configuration files generated by newer clients, as
they had a bug where they could only understand "0" and "1".

common/rfb/Configuration.cxx

@@ -274,15 +274,15 @@ bool BoolParameter::setParam() {
 void BoolParameter::setParam(bool b) {
   if (immutable) return;
   value = b;
-  vlog.debug("Set %s(Bool) to %d", getName(), value);
+  vlog.debug("Set %s(Bool) to %s", getName(), getValueStr().c_str());
 }
 
 std::string BoolParameter::getDefaultStr() const {
-  return def_value ? "1" : "0";
+  return def_value ? "on" : "off";
 }
 
 std::string BoolParameter::getValueStr() const {
-  return value ? "1" : "0";
+  return value ? "on" : "off";
 }
 
 BoolParameter::operator bool() const {