Implement non-internal ivecs

Vectors are now similar to our old, pre-internal vectors, except that
they are uniquely owned, not refcounted.

Their name should probably change too, then. I've renamed them to vec
in the runtime, will do so throughout the compiler later.

src/lib/run_program.rs

@@ -27,7 +27,8 @@ fn spawn_process(prog: &istr, args: &[istr], in_fd: int, out_fd: int,
     // pointer to its buffer
     let argv = arg_vec(prog, args);
     let pid =
-        rustrt::rust_run_program(vec::to_ptr(argv), in_fd, out_fd, err_fd);
+        rustrt::rust_run_program(vec::unsafe::to_ptr(argv),
+                                 in_fd, out_fd, err_fd);
     ret pid;
 }