Auto merge of #5283 - matklad:better-assertion, r=matklad
authorbors <bors@rust-lang.org>
Tue, 3 Apr 2018 08:19:41 +0000 (08:19 +0000)
committerbors <bors@rust-lang.org>
Tue, 3 Apr 2018 08:19:41 +0000 (08:19 +0000)
Make assertion more informative

This assertion triggers when I try to build Cargo simultaneosly on
linux host and windows VM via a shared folder, but it's not clear
what is going on.


Trivial merge