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).
configure: Fix passing multiple target and host triples.
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
configure: Remove legacy triple flags.
auto merge of #10220 : luqmana/rust/con, r=brson

Previously we were actually overwriting `CFG_{HOST,TARGET,BUILD}` with `CFG_{HOST,TARGET,BUILD}_TRIPLE(S)` since configure tested for the legacy one by checking if it was empty which would never be the case. That meant it wouldn't split up multiple triples and just treat it as one long triple.

This pull also fixes the rules that were changed when librustuv was added to use the right CFG_ vars and removes the legacy flags.
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
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