Append missing padding after last field of struct

This patch fixes issue #13186.

When generating constant expression for enum, it is possible that
alignment of expression may be not equal to alignment of type.  In that
case space after last struct field must be padded to match size of value
and size of struct. This commit adds that padding.

See detailed explanation in src/test/run-pass/trans-tag-static-padding.rs
Be more clear about what this lambda expression does
Give more explanation when introducing closures
Demonstrate accessing external variable in first example
Some more closure changes
rustc: Don't die on 0-length pattern idents

These often crop up when using default methods that don't actually bind their
argument names.

Closes #13775
Fix typo
Remove extra semicolons
Suggested revisions to PR 13676.

Most important: distinguish function decl sugar for omitting `-> ()`
from type inference on closures.  I also tried to add a couple more
examples to further emphasize this distinction.  Note that this sugar
(of omitting `-> ()`) is actually already briefly mentioned in an
earlier section, so it is a little tricky deciding whether to put more
material here, or to move it up to the previous section.

Other drive-by fixes:

 * Fix the line length of the code blocks to fit in the width provided
   in the rendered HTML

 * Some minor revisions to wording (e.g. try to clarify in some cases
   where a type mismatch is arising).
native: Always open a file with Open/Write modes

Previously, windows was using the CREATE_NEW flag which fails if the file
previously existed, which differed from the unix semantics. This alters the
opening to use the OPEN_ALWAYS flag to mirror the unix semantics.

Closes #13861
Merge pull request #1 from pnkfelix/clarify-omit-unit-vs-inference

Suggested revisions to PR 13676.
Add a `graphviz` crate for making .dot files to layout and render graphs.
Updated maybe_owned_vec with review feedback.

Namely:

 * Added conversion traits both to and from the various vector types,
   analogous to how `str::MaybeOwned` works with `str::IntoMaybeOwned`
   and `str::Str`.  This led me to add the `FixedLen` variant of
   `MaybeOwnedVector` for interoperability with `std::slice`.

 * Revised client example code to make use of `into_maybe_owned`

 * Added implementations of `Show` and `CloneableVector` for
   `MaybeOwnedVector`.

 * As suggested by kballard, added `into_vec` method that is analogous
   to `CloneableVector::into_owned` except it produces a `Vec` rather
   than a `~[T]`.
rustc: Remove the session building_library flag

This has long since not been too relevant since the introduction of many crate
type outputs. This commit removes the flag entirely, adjusting all logic to do
the most reasonable thing when building both a library and an executable.

Closes #13337
Recommend autoload instead of require

Lazy loading with autoload will result in faster startup time for Emacs
users and is generally the recommended approach for major modes.
shootout-spectralnorm tweaks

- using libgreen to optimize CPU usage
- less tasks to limit wasted resources

Here, on a one core 2 threads CPU, new version is ~1.2 faster.  May
be better with more core.
Remove/Update dead links on Tasks guide.
add back `noalias` to `&mut T` pointer parameters

This was removed because these could alias with `&const T` or `@mut T`
and those are now gone from the language. There are still aliasing
issues within local scopes, but this is correct for function parameters.

This also removes the no-op `noalias` marker on proc (not a pointer) and
leaves out the mention of #6750 because real type-based alias analysis
is not within the scope of best effort usage of the `noalias` attribute.

Test case:

    pub fn foo(x: &mut &mut u32) {
        **x = 5;
        **x = 5;
    }

Before:

    define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** nocapture readonly) unnamed_addr #0 {
    entry-block:
      %1 = load i32** %0, align 8
      store i32 5, i32* %1, align 4
      %2 = load i32** %0, align 8
      store i32 5, i32* %2, align 4
      ret void
    }

After:

    define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** noalias nocapture readonly) unnamed_addr #0 {
    entry-block:
      %1 = load i32** %0, align 8
      store i32 5, i32* %1, align 4
      ret void
    }

Closes #12436
Add missing cases to the type_limits lint

and exhaustive testing for the `u8` type.
Remove two useless comparisons

according to the updated type_limits lint.