Removed wxLB_MULTIPLE from multiListBox props
Removed wxLB_MULTIPLE from multiListBox props

wxLB_EXTENDED is a superset of wxLB_MULTIPLE.
Specifying both wxLB_MULTIPLE and wxLB_EXTENDED leads to a failing assert in wxWidgets code:
 - msw\listbox.cpp
 - osx\checklst_osx.cpp
 - osx\listbox_osx.cpp

ekmett/wxHaskell,Proclivis/wxHaskell,ekmett/wxHaskell,sherwoodwang/wxHaskell,Proclivis/wxHaskell,sherwoodwang/wxHaskell,Proclivis/wxHaskell,sherwoodwang/wxHaskell,sherwoodwang/wxHaskell,Proclivis/wxHaskell,ekmett/wxHaskell