Overload operator<< for UnknownElement as gcc complains about abiguous calls otherwise

Originally committed to SVN as r6024.

aegisub/libaegisub/include/libaegisub/cajun/writer.h

@@ -11,8 +11,11 @@ Author: Terry Caton
 #include "elements.h"
 #include "visitor.h"
 
-namespace json
-{
+#ifndef LAGI_PRE
+#include <ostream>
+#endif
+
+namespace json {
 
 class Writer : private ConstVisitor {
 	Writer(std::ostream& ostr);
@@ -45,5 +48,10 @@ public:
 	}
 };
 
+inline std::ostream& operator <<(std::ostream& ostr, UnknownElement const& elementRoot) {
+    Writer::Write(elementRoot, ostr);
+    return ostr;
+}
+
 
 } // End namespace