Update extra.cpp
Update extra.cpp

Replaced some incorrect long variables/casts to wxIntPtr. On 64-bit wxIntPtr will be a "long long int" causing compile errors.
ekmett/wxHaskell,Proclivis/wxHaskell,ekmett/wxHaskell,sherwoodwang/wxHaskell,ekmett/wxHaskell,sherwoodwang/wxHaskell,Proclivis/wxHaskell,Proclivis/wxHaskell,Proclivis/wxHaskell,sherwoodwang/wxHaskell,sherwoodwang/wxHaskell