Remove IterToGlibPtr and implement ToGlibPtr on slices instead
Remove IterToGlibPtr and implement ToGlibPtr on slices instead

IterToGlibPtr was an attempt to work around the conflicting blanket implementations problem but it appears to be insufficient.
Until the sys crates learn to specify the container types more precisely, we'll have to live without generic impls.

gkoz/rust-gnome-glib,rust-gnome/glib,Susurrus/glib,EPashkin/rust-gnome-glib,gkoz/gtk-rs-glib