fileinput failure on OS X bot

[thestinger]

http://buildbot.rust-lang.org/builders/auto-mac/builds/739/steps/test/logs/stdio

This didn't happen when I did a retry, so it's not a consistently failing test.

[ILyoan]

I think this was because two tests were using the same file name. so the test could fail occassionally.
53232f7 will fix this

closing.