Fix menu popup function
Fix menu popup function

There was an API break in recent gtk versions:
https://bugzilla.gnome.org/show_bug.cgi?id=674537
so adjust testGtk.hs accordingly.

hamishmack/haskell-gi,ford-prefect/haskell-gi,hamishmack/haskell-gi-base,ford-prefect/haskell-gi,hamishmack/haskell-gi