OCALLINTER, as well as ODEFER/OPROC with OCALLMETH/OCALLINTER.

Move all the call logic to its own routine, a lot of the
code is shared.

Change-Id: Ieac59596165e434cc6d1d7b5e46b78957e9c5ed3
Reviewed-on: https://go-review.googlesource.com/14464Reviewed-by: Todd Neal <todd@tneal.org>
Reviewed-by: David Chase <drchase@google.com>