issue9355 generated a file a.[568] in test/ directory and left it there.
For tests like these, it is best to chdir to a test specific directory
before generating any temporary files, since the tests are running
in parallel and might otherwise race with each other for the same files.

Change-Id: I58d96256d4d8ee3fda70d81077f19006064a7425
Reviewed-on: https://go-review.googlesource.com/3813Reviewed-by: Ian Lance Taylor <iant@golang.org>