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.h

@@ -41,6 +41,7 @@ int vncSetParam(const char *name, const char *value);
 int vncSetParamSimple(const char *nameAndValue);
 char* vncGetParam(const char *name);
 const char* vncGetParamDesc(const char *name);
+int vncIsParamBool(const char *name);
 
 int vncGetParamCount(void);
 char *vncGetParamList(void);