Fix for missing Copy on shader::Buffer

[bvssvni]

The end of a rather long list of errors:

src/minecraft/region.rs:147:41: 147:50 error: the trait `core::kinds::Copy` is not implemented for the type `shader::Buffer`
src/minecraft/region.rs:147             buffers: Array::from_fn(|_| Cell::new(None)),
                                                                    ^~~~~~~~~
src/minecraft/region.rs:147:41: 147:50 note: required by `core::cell::Cell<T>::new`
src/minecraft/region.rs:147             buffers: Array::from_fn(|_| Cell::new(None)),
                                                                    ^~~~~~~~~
src/main.rs:288:38: 288:43 error: type `&core::cell::Cell<core::option::Option<shader::Buffer>>` does not implement any method in scope named `get`
src/main.rs:288                         match buffer.get() {
                                                     ^~~~~
src/main.rs:296:32: 298:27 error: type `&core::cell::Cell<core::option::Option<shader::Buffer>>` does not implement any method in scope named `set`
src/main.rs:296                         buffer.set(Some(
src/main.rs:297                             renderer.create_buffer(staging_buffer.as_slice())
src/main.rs:298                         ));
error: aborting due to 98 previous errors
Could not compile `hematite`.

When trying to add a #[deriving(Copy)] on shader::Buffer it complains that buf: gfx::BufferHandle<Vertex> is not Copy.

[bvssvni]

This was fixed, while the current problem is related but not the same. Closing.