The only slice/interface comparisons that reach
the backend are comparisons to nil.

Funcs, maps, and channels are references types,
so pointer equality is enough.

Change-Id: I60a71da46a36202e9bd62ed370ab7d7f2e2800e7
Reviewed-on: https://go-review.googlesource.com/12715Reviewed-by: Keith Randall <khr@golang.org>