Fixes #6894
Private DrawLabel() method renamed to _DrawLabel() and rest of drawing
code moved to new private method _DrawMenuField(). These methods both
check to make sure that they are drawing in a valid rect that intersects
updateRect.
When label or menu is selected Draw a the label background in the selected
menu color matching the behavior of BeOS R5.
_DrawLabel() calls be_control_look->DrawLabel()
Update copyright year in MenuField.h
9422c92ea3