gc: allow implicit conversion of *[10]int -> []int when used as arg to copy.
gc: allow implicit conversion of *[10]int -> []int
when used as arg to copy.

R=ken2
http://codereview.appspot.com/157071
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go