This reverts commit 9b9170f9.

You can now say

    let {bcx, val} = some_result_returner();

Similar for loop variables. Assigning to such variables is not safe
yet. Function arguments also remain a TODO.

(Also, some formatting and long-string cleanup.)

(in the pretty-printer)

(And extra parens around else-if tests)

(Methods still don't seem to have constraints associated with them.
Method types do, so I guess this is a TODO.)

Handle hardbreaks at bol slightly better, including break_offset calls (tuck offset into previous hardbreak).

Adjust pp interface to that printing a crate (an reproducing literals/comments) takes a reader, not just a filename. Fixes first big pp-fuzzer bug.

This adds parser support and most of the machinery for

    auto x = 10, y = 20;

However, the above still goes wrong somewhere in typestate, causing
the state checker to believe only the last variable in the list is
initialized after the statement.

Tim, if you have a moment, could you go over the changes to the tstate
code in this patch and see where I'm going wrong?

Multi-var-decls without the typestate extension

Add a loop

We should probably do another pretty-printing pass soon.

Programs with constrained types now parse and typecheck, but
typestate doesn't check them specially, so the one relevant test
case so far is XFAILed.

Also rewrote all of the constraint-related data structures in the
process (again), for some reason. I got rid of a superfluous
data structure in the context that was mapping front-end constraints
to resolved constraints, instead handling constraints in the same
way in which everything else gets resolved.

Introduce a proto_to_str function to find the string representation of a given
proto instead of casing on the proto in multiple places.