Auto merge of #2448 - alexcrichton:docs-dirty, r=brson
authorbors <bors@rust-lang.org>
Thu, 10 Mar 2016 01:18:27 +0000 (17:18 -0800)
committerbors <bors@rust-lang.org>
Thu, 10 Mar 2016 01:18:27 +0000 (17:18 -0800)
Fix rerunning rustdoc when output deleted

If `crate/index.html` is missing, we need to rerun rustdoc!

Closes #2379


Trivial merge