#378 LoadDialogResource doesn't recognize extended dialogs

[Roger Upole]

Extended dialog templates have a different format
than regular dialogs. (DLGTEMPLATEEX, which is apparently not actually defined as a struct anywhere)
According to MSDN, they can be identified by 0xffff in the second WORD of the data.
Currently win32ui tries to treat them as a regular
dialog resource and returns bad data.

>>> win32ui.LoadDialogResource(win32ui.IDD_ABOUTBOX)
[['About Pythonwin', (0, 192, -32568, 4), 4294901761, 0, None, '"\x16ät', 0]]

For right now, I'm just going to check for the 0xffff and return NotImplementedError.