Auto merge of #3875 - matklad:unused-replace, r=alexcrichton
authorbors <bors@rust-lang.org>
Thu, 30 Mar 2017 18:10:07 +0000 (18:10 +0000)
committerbors <bors@rust-lang.org>
Thu, 30 Mar 2017 18:10:07 +0000 (18:10 +0000)
Fix false positive about unused replace

closes #3861
@chriscoomber thanks for the great repro!


Trivial merge