Allow index buffer creation from slice
Allow index buffer creation from slice

caldwell/glium,tomaka/glium,nicokoch/glium,binsoftware/glium,christopheraugustus/glium,bvssvni/glium,acolley/glium,rozaliev/glium,sdotz/glium,TyOverby/glium,glium/glium,cpjreynolds/glium,carbidegames/glium