This comes with a terminology change. All linkage-symbols are 'extern'
now, including rust syms in other crates. Some extern ABIs are
merely "foreign". The term "native" is retired, not clear/useful.
What was "crust" is now "extern" applied to a _definition_. This
is a bit of an overloading, but should be unambiguous: it means
that the definition should be made available to some non-rust ABI.
Most could use the each method, but because of the hack used to
disambiguate old- and new-style loops, some had to use vec::each.
(This hack will go away soon.)
Issue #1619
