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
use option_env! instead of env!
Pre-step towards issue #12624 and others: Introduce ExprUseVisitor, remove the
moves computation. ExprUseVisitor is a visitor that walks the AST for a
function and calls a delegate to inform it where borrows, copies, and moves
occur.

In this patch, I rewrite the gather_loans visitor to use ExprUseVisitor, but in
future patches, I think we could rewrite regionck, check_loans, and possibly
other passes to use it as well. This would refactor the repeated code between
those places that tries to determine where copies/moves/etc occur.
Convert delegate to use an object type and remove FIXME from closed issue
rustdoc: refactor and unstyle inline section headers
std: Add experimental networking methods

The underlying I/O objects implement a good deal of various options here and
there for tuning network sockets and how they perform. Most of this is a relic
of "whatever libuv provides", but these options are genuinely useful.

It is unclear at this time whether these options should be well supported or
not, or whether they have correct names or not. For now, I believe it's better
to expose the functionality than to not, but all new methods are added with
an #[experimental] annotation.
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
doc: perform some 80-chars wrappings
rustdoc: style tweaks
Add a streaming parser to serialize::json.
Fix a code formatting issue in json.rs
Update libworkcache with libserialize's json changes
Fix test issue-4016.rs with the json API change
Remove default method implementations
rustdoc: fix a few inconsistencies
Provide an implementation of DoubleEndedIterator for the results of &[T]::split and &[T]::rsplit

This makes the splitting functions in std::slice return DoubleEndedIterators. Unfortunately,
splitn and rsplitn cannot provide such an interface and so must return different types. As a
result, the following changes were made:

* RevSplits was removed in favor of explicitly using Rev
* Splits can no longer bound the number of splits done
* Splits now implements DoubleEndedIterator
* SplitsN was added, taking the role of what both Splits and RevSplits used to be
* rsplit returns Rev<Splits<'a, T>> instead of RevSplits<'a, T>
* splitn returns SplitsN<'a, T> instead of Splits<'a, T>
* rsplitn returns SplitsN<'a, T> instead of RevSplits<'a, T>

All functions that were previously implemented on each return value still are, so outside of changing
of type annotations, existing code should work out of the box. In the rare case that code relied
on the return types of split and splitn or of rsplit and rsplitn being the same, the previous
behavior can be emulated by calling splitn or rsplitn with a bount of uint::MAX.

The value of this change comes in multiple parts:

* Consistency. The splitting code in std::str is structured similarly to the new slice splitting code,
  having separate CharSplits and CharSplitsN types.
* Smaller API. Although this commit doesn't implement it, using a DoubleEndedIterator for splitting
  means that rsplit, path::RevComponents, path::RevStrComponents, Path::rev_components, and
  Path::rev_str_components are no longer needed - they can be emulated simply with .rev().
* Power. DoubleEndedIterators are able to traverse the list from both sides at once instead of only
  forwards or backwards.
* Efficiency. For the common case of using split instead of splitn, the iterator is slightly smaller
  and slightly faster.

[breaking-change]