fix missing_doc lint on private traits

Fixes #10069.
Name the rustc task 'rustc'
Reduce the aggressiveness of reachability

Previously, all functions called by a reachable function were considered
reachable, but this is only the case if the original function was possibly
inlineable (if it's type generic or #[inline]-flagged).
Drop struct fields if the user destructor fails

This commit changes drop glue generated for structs to use the invoke LLVM
instruction instead of call. What this means is that if the user destructor
triggers an unwinding, then the fields of the struct will still ge dropped.

This is not an attempt to support failing while failing, as that's mostly a
problem of runtime support. This is more of an issue of soundness in making sure
that destructors are appropriately run. The test included fails before this
commit, and only has one call to fail!(), yet it doesn't destroy its struct
fields.
std::rand: Move distributions to a subfolder.
std::rand: Implement the Gamma distribution.
std::rand: share the benchmark counter among the whole module tree.
Fix typo in to_digit
Bump required pandoc version to 1.9.

Earlier versions of pandoc don't have the default.html5 and thus,
building the docs fail.

Signed-off-by: Noufal Ibrahim <noufal@nibrahim.net.in>
Use consistent capitalization in makefile errors

In Rust we don't like capital letters.
auto merge of #10215 : brson/rust/rustctask, r=thestinger
Register new snapshots

Closes #2240
auto merge of #10223 : huonw/rust/gamma, r=cmr

Implements the [Gamma distribution](https://en.wikipedia.org/wiki/Gamma_distribution), using the algorithm described by Marsaglia & Tsang 2000[1]. I added tests checking that the mean and variance of this implementation is as expected for a range of values of the parameters in https://github.com/huonw/random-tests/commit/5d87c00a0fb69c8fa173593714cef76ddfddb651 (they pass locally, but obviously won't even build on Travis until this is merged).

Also, moves `std::rand::distributions` to a subfolder, and performs a minor clean-up of the benchmarking (makes the number of iterations shared by the whole `std::rand` subtree).

[1]: George Marsaglia and Wai Wan Tsang. 2000. "A Simple Method for Generating Gamma Variables" *ACM Trans. Math. Softw.* 26, 3 (September 2000), 363-372. DOI:[10.1145/358407.358414](http://doi.acm.org/10.1145/358407.358414).
Fix installation with DESTDIR
auto merge of #10222 : nibrahim/rust/docfix, r=brson

Earlier versions of pandoc don't have the `default.html5` template file. When `make docs` is run, the build process fails with this message.

    pandoc: doc/rust.html
    pandoc: /usr/share/pandoc-1.8.2.1/templates/default.html5: openFile: does not exist (No such file or directory)
    
    node.js:201
            throw e; // process.nextTick error, or 'error' event on first tick
                  ^
    Error: write EPIPE
        at errnoException (net.js:670:11)
        at Object.afterWrite [as oncomplete] (net.js:503:19)
    make: *** [doc/rust.html] Error 1
Stop propagating link arguments across crates

This is a fairly brittle modle that doesn't scale well across many crates. It's
unlikely that all of the downstream crates will have all of the original native
dependencies of all the upstream crates. In the case that FFI functions are
reachable, then it should be the responsibility of the downstream crate to link
against the correct library, or the upstream crate should prevent the functions
from being reachable.
Statically link sundown to librustdoc

Closes #10103
auto merge of #10232 : brson/rust/destdir, r=thestinger
Rustdoc: Properly strip private modules

A private module will survive the strip-private pass if it contains
trait implementations, which aren't stripped until a separate pass in
render.
auto merge of #10225 : Jurily/rust/master, r=alexcrichton