Tolerate specifying -BoolParam 0 and similar

This is needed by vncserver which doesn't know which parameters are
boolean, and it cannot use the -Param=Value form as that isn't tolerated
by the Xorg code.

unix/xserver/hw/vnc/RFBGlue.cc

@@ -143,6 +143,22 @@ const char* vncGetParamDesc(const char *name)
   return param->getDescription();
 }
 
+int vncIsParamBool(const char *name)
+{
+  VoidParameter *param;
+  BoolParameter *bparam;
+
+  param = rfb::Configuration::getParam(name);
+  if (param == NULL)
+    return false;
+
+  bparam = dynamic_cast<BoolParameter*>(param);
+  if (bparam == NULL)
+    return false;
+
+  return true;
+}
+
 int vncGetParamCount(void)
 {
   int count;