GitHub: close #127
Because Init_gdk_screen() is conflicted with the same name function in
Ruby/GDK3 on Mac OS X.
We don't extern internal Init_*() functions by G_GNUC_INTERNAL but it
is not worked on Mac OS X. Because clang is used instead of gcc on Mac
Reported by Sergio Campama. Thanks!!!
Backtrace is provided by Watson. Thanks!!!