Handle infinite-loop poststate correctly in typestate

If control passes an infinite loop (that doesn't have non-local
exits), then everything is true.

Author: catamorphism

src/rustc/middle/tstate/states.rs

@@ -554,7 +554,7 @@ fn find_pre_post_state_expr(fcx: fn_ctxt, pres: prestate, e: @expr) -> bool {
             ret changed | set_poststate_ann(fcx.ccx, e.id, pres);
         } else {
             ret changed | set_poststate_ann(fcx.ccx, e.id,
-                             block_poststate(fcx.ccx, body));
+                                            false_postcond(num_constrs));
         }
       }
       expr_for(d, index, body) {

src/test/compile-fail/while-loop-pred-constraints.rs

@@ -11,6 +11,6 @@ fn main() {
     check (even(y));
     loop {
         print_even(y);
-        loop { loop { loop { y += x; } } }
+        while true { while true { while true { y += x; } } }
     }
 }