suggest adding a where-clause when that can help

suggest adding a where-clause when there is an unmet trait-bound that
can be satisfied if some type can implement it.

src/doc/book/closures.md

@@ -371,14 +371,13 @@ assert_eq!(6, answer);
 This gives us these long, related errors:
 
 ```text
-error: the trait `core::marker::Sized` is not implemented for the type
-`core::ops::Fn(i32) -> i32` [E0277]
+error: the predicate `core::ops::Fn(i32) -> i32 : core::marker::Sized` is not satisfied [E0277]
 fn factory() -> (Fn(i32) -> i32) {
                 ^~~~~~~~~~~~~~~~
 note: `core::ops::Fn(i32) -> i32` does not have a constant size known at compile-time
 fn factory() -> (Fn(i32) -> i32) {
                 ^~~~~~~~~~~~~~~~
-error: the trait `core::marker::Sized` is not implemented for the type `core::ops::Fn(i32) -> i32` [E0277]
+error: the predicate `core::ops::Fn(i32) -> i32 : core::marker::Sized` is not satisfied [E0277]
 let f = factory();
     ^
 note: `core::ops::Fn(i32) -> i32` does not have a constant size known at compile-time

src/doc/book/concurrency.md

@@ -231,8 +231,8 @@ fn main() {
 This won't work, however, and will give us the error:
 
 ```text
-13:9: 13:22 error: the trait `core::marker::Send` is not
-            implemented for the type `alloc::rc::Rc<collections::vec::Vec<i32>>`
+13:9: 13:22 error: the predicate `alloc::rc::Rc<collections::vec::Vec<i32>> : core::marker::Send`
+            is not satisfied
 ...
 13:9: 13:22 note: `alloc::rc::Rc<collections::vec::Vec<i32>>`
             cannot be sent between threads safely

src/doc/book/traits.md

@@ -154,7 +154,7 @@ print_area(5);
 We get a compile-time error:
 
 ```text
-error: the trait `HasArea` is not implemented for the type `_` [E0277]
+error: the predicate `_ : HasArea` is not satisfied [E0277]
 ```
 
 ## Trait bounds on generic structs
@@ -496,7 +496,7 @@ impl FooBar for Baz {
 If we forget to implement `Foo`, Rust will tell us:
 
 ```text
-error: the trait `main::Foo` is not implemented for the type `main::Baz` [E0277]
+error: the predicate `main::Baz : main::Foo` is not satisfied [E0277]
 ```
 
 # Deriving

src/doc/book/vectors.md

@@ -56,8 +56,8 @@ v[j];
 Indexing with a non-`usize` type gives an error that looks like this:
 
 ```text
-error: the trait `core::ops::Index<i32>` is not implemented for the type
-`collections::vec::Vec<_>` [E0277]
+error: the predicate `collections::vec::Vec<_> : core::ops::Index<i32>`
+is not satisfied [E0277]
 v[j];
 ^~~~
 note: the type `collections::vec::Vec<_>` cannot be indexed by `i32`

src/doc/nomicon/coercions.md

@@ -64,7 +64,7 @@ fn main() {
 ```
 
 ```text
-<anon>:10:5: 10:8 error: the trait `Trait` is not implemented for the type `&mut i32` [E0277]
+<anon>:10:5: 10:8 error: the predicate `&mut i32 : Trait` is not satisfied [E0277]
 <anon>:10     foo(t);
               ^~~
 ```