The code example in the trait documentation of ExactSizeIterator
has an incorrect implementation of the len method that does not return
the number of times the example iterator 'Counter' will iterate. This
may confuse readers of the docs as the example code will compile but 
doesn't uphold the trait's contract.

This is easily fixed by modifying the implementation of len and changing
the assert statement to actually assert the correct behaviour. I also
slightly modified a code comment to better reflect what the method 
returns.

Given the following statement

```rust
pub (a) fn afn() {}
```

Provide the following diagnostic:

```rust
error: incorrect restriction in `pub`
  --> file.rs:15:1
   |
15 | pub (a) fn afn() {}
   | ^^^^^^^
   |
   = help: some valid visibility restrictions are:
           `pub(crate)`: visible only on the current crate
           `pub(super)`: visible only in the current module's parent
           `pub(in path::to::module)`: visible only on the specified path
help: to make this visible only to module `a`, add `in` before the path:
   | pub (in a) fn afn() {}
```

Remove cruft from old `pub(path)` syntax.

Use the "official" cross compiler for NetBSD

The current NetBSD cross compiler is lacking, for example `std::thread` is not available (which causes problems for LLVM 4.0). This PR uses the official netbsd build system to compiler the cross compiler.

@alexcrichton: Can you please mirror `ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-7.0/source/sets/{src,gnusrc,sharesrc,syssrc}.tgz`. (Optionally you may want to use NetBSD versions 7.0.2 or 7.1, in that case you'll probably want to update the binary downloads used today as well).

I'll update the URL's afterwards (or feel free to use "allow edits from maintainers").

r? @alexcrichton

…nkov

Add diagnostic for incorrect `pub (restriction)`

Given the following statement

```rust
pub (a) fn afn() {}
```

Provide the following diagnostic:

```rust
error: incorrect restriction in `pub`
  --> file.rs:15:1
   |
15 | pub (a) fn afn() {}
   |     ^^^
   |
   = help: some valid visibility restrictions are:
           `pub(crate)`: visible only on the current crate
           `pub(super)`: visible only in the current module's parent
           `pub(in path::to::module)`: visible only on the specified path
help: to make this visible only to module `a`, add `in` before the path:
   | pub (in a) fn afn() {}
```

Follow up to rust-lang#40340, fix rust-lang#40599, cc rust-lang#32409.

…atsakis

On-demandify associated item retrieval

Part of rust-lang#40614.

I also started converting `adt_def`, but I decided to open a PR with just this bit first to make sure I'm going about this correctly.

r? @nikomatsakis

Fix doc error for ExactSizeIterator

The code example in the trait documentation of ExactSizeIterator
has an incorrect implementation of the len method that does not return
the number of times the example iterator 'Counter' will iterate. This
may confuse readers of the docs as the example code will compile but
doesn't uphold the trait's contract.

This is easily fixed by modifying the implementation of len and changing
the assert statement to actually assert the correct behaviour. I also
slightly modified a code comment to better reflect what the method
returns.

…n-message, r=brson

Change object safety violation message

Hello!

This is my first pull request to rust so hopefully all goes well. This PR should fix issue rust-lang#40670. I changed the error message in object_safety.rs and the corresponding compile-fail test in object-safety-supertrait-mentions-Self.rs.

Once the changes were made, I ran ```python x.py test src/tools/tidy``` and ```python x.py test```. Tidy passed and the compile-fail tests passed, however the test suite failed on the tcp tests as my machine has IPv6 disabled. I'm not sure what to do in this case besides letting travis run the suite against my changes. Please let me know if there's anything I can do to help further.

Thanks!
Mandeep