Fix for bug #10

Recently, most packages which were previously depending on `mesa`
switched to `libGL`, which is supposed to find the host system opengl
library, as long as it is available in the library search path.

default.nix

@@ -74,6 +74,7 @@ rec {
       cat > $out/bin/nixGLIntel << FOO
       #!/usr/bin/env sh
       export LIBGL_DRIVERS_PATH=${mesa_drivers}/lib/dri
+      export LD_LIBRARY_PATH=${mesa_drivers}/lib
       "\$@"
       FOO