riched20: register ListBox & ComboBox classes

[Cihan Altinay]

(This time with booleans as suggested by Alexandre)

This patch partially implements the undocumented REExtendedRegisterClass()
function by registering the two missing classes. That way MS Office 2003 and
probably other programs that rely on these classes display dialogs
completely which were empty before. The return value corresponds to native
Windows.

Changelog:
    Cihan Altinay 
    Partially implement REExtendedRegisterClass() to register missing window
    classes so that applications relying on them don't get confused.