rt: Remove the now-unused upcall_ivec_resize and upcall_ivec_spill, which allocated from the wrong heap

Somehow this has been disabled forever

Assignments and moves with a simple local variable reference on the
RHS now propagate any typestate constraints the RHS was involved
in to the LHS. Swaps where both sides are local variables
exchange the constraints.

This was a pain in the butt and I'm still not proud of the resulting
code. Needs refactoring like whoa.

Instead of noting where the imported things were defined, note where they were
imported. This is more useful and avoids issue #482.

This has been fixed by a mystery hacker.

rustc: Fix a level-of-indirection problem by using size_of() to compute dynamically sized interior vector element sizes instead of field_of_tydesc()

(Incidentally, what's the right way to test changes to the
pretty-printer?  There has to be a better way than what I did, which
was to log_err the results of expr_to_str as exprs passed through
trans and glance at the output.)

Once populated, this will allow us to load type info for types defined in
external crates referenced by other external crates.

the common case of wanting to link statically with the project's libraries
but dynamically with the system ones.