Remove the synthetic "region bound" from closures and instead update how

type-outlives works for closure types so that it ensures that all upvars
outlive the region in question. This gives the same guarantees but
without introducing artificial regions (and gives better error messages
to boot).

src/test/compile-fail/issue-4335.rs

@@ -14,7 +14,9 @@
 fn id<T>(t: T) -> T { t }
 
 fn f<'r, T>(v: &'r T) -> Box<FnMut() -> T + 'r> {
-    id(box || *v) //~ ERROR cannot infer
+    id(box || *v)
+        //~^ ERROR `v` does not live long enough
+        //~| ERROR cannot move out of borrowed content
 }
 
 fn main() {

src/test/compile-fail/regions-proc-bound-capture.rs

@@ -18,7 +18,7 @@ fn borrowed_proc<'a>(x: &'a isize) -> Box<FnMut()->(isize) + 'a> {
 
 fn static_proc(x: &isize) -> Box<FnMut()->(isize) + 'static> {
     // This is illegal, because the region bound on `proc` is 'static.
-    box move|| { *x } //~ ERROR cannot infer
+    box move|| { *x } //~ ERROR captured variable `x` does not outlive the enclosing closure
 }
 
 fn main() { }

src/test/compile-fail/regions-steal-closure.rs

@@ -20,9 +20,9 @@ fn box_it<'r>(x: Box<FnMut() + 'r>) -> closure_box<'r> {
 }
 
 fn main() {
-    let cl_box = {
+    let mut cl_box = {
         let mut i = 3;
-        box_it(box || i += 1) //~ ERROR cannot infer
+        box_it(box || i += 1) //~ ERROR `i` does not live long enough
     };
     cl_box.cl.call_mut(());
 }

src/test/compile-fail/send-is-not-static-ensures-scoping.rs

@@ -13,9 +13,10 @@ use std::thread;
 fn main() {
     let bad = {
         let x = 1;
-        let y = &x;
+        let y = &x; //~ ERROR `x` does not live long enough
 
-        thread::scoped(|| { //~ ERROR cannot infer an appropriate lifetime
+        thread::scoped(|| {
+            //~^ ERROR `y` does not live long enough
             let _z = y;
         })
     };

src/test/compile-fail/unboxed-closure-region.rs

@@ -15,6 +15,6 @@
 fn main() {
     let _f = {
         let x = 0_usize;
-        || x //~ ERROR cannot infer an appropriate lifetime due to conflicting requirements
+        || x //~ ERROR `x` does not live long enough
     };
 }