So that the tinderboxes can go green again. Patrick, please look into
this at some point.

This is accepted everywhere, since just passing a pointer is safe.

Introduce an ext_ctxt record to provide a span_err method for use while
expanding syntax extensions. Hopefully it will be useful for other things.

Issue rust-lang#444

Issue rust-lang#444

After this we can remove the parser from the syntax extensions, at least for
now.

Eventually extensions will probably need access to the parser again, but it'll
be in a different form.

This is not obnoxious now that logging is off by default

Issue rust-lang#444

sess.span_err instead of 'fail'.  (issue rust-lang#444)

This litters aberrations like 'alt({foo.bar}) { ... }' and f({*baz})
though the code (mostly in trans.rs). These are a way to explicitly
copy the given value so that it can be safely aliased. At some point
we'll probably want a more explicit copy operator.

The alias checker works by ensuring that any value to which an alias
is created is rooted in some way that ensures it outlives the alias.

It is now disallowed to create an alias to the content of a mutable
box, or to a box hanging off a mutable field. There is also machinery
in place to prevent assignment to local variables whenever they are
the root of a live alias.

…ing.

…is a step

in getting a driver that works on all linux systems.

Sorry for the linker hacks, I will remove them after snapshotting a new compiler.

calls (issue rust-lang#444).

…ersion numbers.

… and ty_local.

Sorry, big perf regression; will fix soon.

…urning tinderbox.

…anymore.

…ught; put out burning tinderbox

…remove mo_either

… has vars before folding over it; also remove some debug code. 2x typechecking speedup.

Some of the vec utilities now only work on immutable vecs, since they
would have to be rewritten to do a lot more copying to be alias-safe.

Some forced copying was added to map.rs, showing a weakness in the
alias checker (or maybe the alias system): when fn args are passed
into a function, calling them must assume all aliases that are not
immutably rooted (directly connected to a local or temporary without
any mutable edges) become invalid. This will be a drag on functional
programming in Rust.

Work around alias issues in the stdlib

The old system tried to ensure that the location an alias pointed at
would retain its type. That turned out to not be strong enough in the
face of aliases to the inside of tags.

The new system instead proves that values pointed to by aliases are
not replaced (or invalidated in some other way) at all. It knows of
two sufficient conditions for this, and tries to prove at least of
them:

A) The alias is 'immutably rooted' in a local, and this local is not
   reassigned for the lifetime of the alias. Immutably rooted means
   the alias refers to the local itself, or to something reachable
   from the local through immutable dereferencing.

B) No value whose type might include the type of the 'inner mutable
   element' of the thing the alias refers to (for example, the box in
   rec(mutable x = @mutable int)) is from the outer scope is accessed
   for the lifetime of the alias. This means for functions, no other
   argument types may include the alias's inner mutable type. For alt,
   for each, and for, it means the body does not refer to any locals
   originating from outside their scope that include this type.

The lifetime of an alias in an alt, for each, or for body is defined
as the range from its definition to its last use, not to the point
where it goes out of scope. This makes working around these
restrictions somewhat less annoying. For example, you can assign to
your alt-ed value you don't refer to any bindings afterwards.

There was a bug that would cause the alias analyser to allow you to
invalidate an alias that was no longer directly referred to, even if
another alias was rooted in it. It now properly tracks dependencies
between live aliases.

Required another case of copying values in map.rs.