- certain code paths were appending to the string without first clearing it.
- some prints were using spaces instead of tabs

Change-Id: I7a3d38289c8206682baf8942abf5a9950a56b449
Reviewed-on: https://go-review.googlesource.com/3511Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Dave Cheney <dave@cheney.net>