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.
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.
auto merge of #10804 : alexcrichton/rust/less-dup, r=pcwalton

This is just an implementation detail of using libuv, so move the libuv-specific
logic into librustuv.
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()
auto merge of #10796 : kballard/rust/revert-new-naming, r=alexcrichton

Rename the `*::init()` functions back to `*::new()`, since `new` is not
going to become a keyword.
Update LLVM and jettison jit support

LLVM's JIT has been updated numerous times, and we haven't been tracking it at
all. The existing LLVM glue code no longer compiles, and the JIT isn't used for
anything currently.

This also rebases out the FixedStackSegment support which we have added to LLVM.
None of this is still in use by the compiler, and there's no need to keep this
functionality around inside of LLVM.

This is needed to unblock #10708 (where we're tripping an LLVM assertion).
Remove unused upcalls

The main one removed is rust_upcall_reset_stack_limit (continuation of #10156),
and this also removes the upcall_trace function. The was hidden behind a
`-Z trace` flag, but if you attempt to use this now you'll get a linker error
because there is no implementation of the 'upcall_trace' function. Due to this
no longer working, I decided to remove it entirely from the compiler (I'm also a
little unsure on what it did in the first place).