-/*
- Creates a hidden window with supplied window proc registering the class for
- it if necesssary (i.e. the first time only). Caller is responsible for
- destroying the window and unregistering the class (note that this must be
- done because wxWidgets may be used as a DLL and so may be loaded/unloaded
- multiple times into/from the same process so we cna't rely on automatic
- Windows class unregistration).
-
- pclassname is a pointer to a caller stored classname, which must initially be
- NULL. classname is the desired wndclass classname. If function successfully
- registers the class, pclassname will be set to classname.
- */