Readd accidentally deleted argument in wxConfig interface

This missing argument was removed in 0c837e5310
and causes the doxygen docs for wxConfigBase to be incorrect and miss
a lot of functions.

interface/wx/config.h

@@ -571,6 +571,7 @@ public:
         @endWxPerlOnly
     */
     bool Read(const wxString& key, wxLongLong_t* ll,
+              wxLongLong_t defaultVal) const;
     /**
         Reads a size_t value, returning @true if the value was found.
         If the value was not found, @a value is not changed.