rustc: Add some suppot for mixing rlibs and dylibs

Currently, rustc requires that a linkage be a product of 100% rlibs or 100%
dylibs. This is to satisfy the requirement that each object appear at most once
in the final output products. This is a bit limiting, and the upcoming libcore
library cannot exist as a dylib, so these rules must change.

The goal of this commit is to enable *some* use cases for mixing rlibs and
dylibs, primarily libcore's use case. It is not targeted at allowing an
exhaustive number of linkage flavors.

There is a new dependency_format module in rustc which calculates what format
each upstream library should be linked as in each output type of the current
unit of compilation. The module itself contains many gory details about what's
going on here.

cc #10729
Generalize stats from f64 to the Float trait
Use is_zero
docs: change compositionality to composability
vim: Fix indentation at global scope after non-semantic ([{/)]}

If an unbalanced [ exists in a string or comment, this should not be
considered when calculating the indent at the top level.

Similarly, when testing for ({/}) to see if we're at the top level to
begin with, strings and comments should be skipped.
Cleanup proc comment in guide-tasks.md.
Reverse #13034

It has been found that #13034 was flawed and caused regression #13867.
This patch reveres the changes made by it except the companion tests.
Adjust codegen logic for range and guarded arms

By carefully distinguishing falling back to the default arm from moving
on to the next pattern, this patch adjusts the codegen logic for range
and guarded arms of pattern matching expression. It is a more
appropriate way of fixing #12582 and #13027 without causing regressions
such as #13867.

Closes #13867
Updated CONTRIBUTING.md for 2014
Allow attributes in std::bitflags::bitflags!

The `std::bitflags::bitflags!` macro did not provide support for
adding attributes to the generated structure or flags, due to
limitations in the parser for macros. This patch works around the
parser limitations by requiring a `flags` keyword in the overall
`bitflags!` invocation, and a `static` keyword for each flag:

    bitflags!(
        #[deriving(Hash)]
        #[doc="Three flags"]
        flags Flags: u32 {
            #[doc="The first flag"]
            static FlagA       = 0x00000001,
            static FlagB       = 0x00000010,
            static FlagC       = 0x00000100
        }
    )
Add (unsafe) coercion from bits to std::bitflags

The intent of `std::bitflags` is to allow building type-safe wrappers
around C-style flags APIs. But in addition to construction these flags
from the Rust side, we need a way to convert them from the C
side. This patch adds a `from_bits` function, which is unsafe since
the bits in question may not represent a valid combination of flags.
Change std::io::FilePermission to a typesafe representation

This patch changes `std::io::FilePermissions` from an exposed `u32`
representation to a typesafe representation (that only allows valid
flag combinations) using the `std::bitflags`, thus ensuring a greater
degree of safety on the Rust side.

Despite the change to the type, most code should continue to work
as-is, sincde the new type provides bit operations in the style of C
flags. To get at the underlying integer representation, use the `bits`
method; to (unsafely) convert to `FilePermissions`, use
`FilePermissions::from_bits`.

Closes #6085.

[breaking-change]
auto merge of #13940 : edwardw/rust/refutable-match, r=pcwalton

By carefully distinguishing falling back to the default arm from moving
on to the next pattern, this patch adjusts the codegen logic for range
and guarded arms of pattern matching expression. It is a more
appropriate way of fixing #12582 and #13027 without causing regressions
such as #13867.
    
Closes #13867
auto merge of #13946 : pnkfelix/rust/fsk-cleanup-proc-comment-in-guide-tasks, r=alexcrichton

Followup to some recent feedback in PR #13676.
Add Richo Healey to contributors
auto merge of #13925 : kballard/rust/vim_indent_bracket_fix, r=thestinger

If an unbalanced [ exists in a string or comment, this should not be
considered when calculating the indent at the top level.

Similarly, when testing for ({/}) to see if we're at the top level to
begin with, strings and comments should be skipped.
auto merge of #13939 : richo/rust/docs/composability, r=thestinger

While there are various references to the work compositionality on the web, I can't find any reference to it being an actual word. My understanding is that composability is what's actually meant here anyway.
Lower armhf target feature to v6.
auto merge of #13952 : aaronraimist/rust/patch-1, r=thestinger
auto merge of #13961 : richo/rust/richo-author, r=alexcrichton

Shamelessly adds myself as a contributor.