Decode a float into integers

The `integer_decode()` function decodes a float (f32/f64)
into integers containing the mantissa, exponent and sign.

It's needed for `rationalize()` implementation of #9838.

The code got ported from ABCL [1].

[1] http://abcl.org/trac/browser/trunk/abcl/src/org/armedbear/lisp/FloatFunctions.java?rev=14465#L94
rewrite of shootout-reverse-complement.rs

This version is inspired by the best version in C by Mr Ledrug,
but without the parallelisation.
rewrite part of the tutorial

This begins a rewrite of some sections the tutorial as an introduction
to concepts through the implementation of a simple data structure. I
think this would be a good way to introduce references, traits and many
other concepts too. For example, the section introducing alternatives to
ownership can demonstrate a persistent list.
auto merge of #10690 : thestinger/rust/doc, r=alexcrichton

This begins a rewrite of some sections the tutorial as an introduction
to concepts through the implementation of a simple data structure. I
think this would be a good way to introduce references, generics, traits
and many other concepts too. For example, the section introducing
alternatives to ownership can demonstrate a persistent list.
auto merge of #10803 : vmx/rust/integer-decode, r=cmr

The `integer_decode()` function decodes a float (f32/f64)
into integers containing the mantissa, exponent and sign.

It's needed for `rationalize()` implementation of #9838.

The code got ported from ABCL [1].

[1] http://abcl.org/trac/browser/trunk/abcl/src/org/armedbear/lisp/FloatFunctions.java?rev=14465#L94

I got the permission to use this code for Rust from Peter Graves (the ABCL copyright holder) . If there's any further IP clearance needed, let me know.
auto merge of #10799 : TeXitoi/rust/shootout-reverse-complement-resurected, r=alexcrichton

This version is inspired by the best version in C by Mr Ledrug,
but without the parallelisation.
Revert "libstd: Change `Path::new` to `Path::init`."

This reverts commit c54427ddfbbab41a39d14f2b1dc4f080cbc2d41b.

Leave the #[ignores] in that were added to rustpkg tests.

Conflicts:
	src/librustc/driver/driver.rs
	src/librustc/metadata/creader.rs
Rename extra::json::*::init() constructors to *::new()
Rename std::rt::deque::*::init() to *::new()