Everything should now call ptr::addr_of instead of
ptr::p2::addr_of. Only the pipes macro code when compiled
by stage0 will call ptr::p2::addr_of. Needs a snapshot to get
rid of that.

Needs a snapshot before this can be completed, because I changed
the mode for conv_poly.

Unfortunately this trips over issue (#3585), where auto-ref isn't
playing nicely with @T implementations. Most serializers don't
care, but prettyprint2 won't properly display "@" until #3585 is
fixed.

This will need a snapshot before we can convert ebml and rustc
to use the new-style serialization.

an explicit variable name. (Step one to changing the defaults)

First step to #3535