Auto merge of #2578 - alexcrichton:test-doc, r=brson
authorbors <bors@rust-lang.org>
Thu, 21 Apr 2016 17:40:42 +0000 (10:40 -0700)
committerbors <bors@rust-lang.org>
Thu, 21 Apr 2016 17:40:42 +0000 (10:40 -0700)
Add `cargo test --doc`

Supports testing only the documentation (like `--lib`, `--bin`, etc).


Trivial merge