tiff: re-organize some test cases, and make comment style consistent.
tiff: re-organize some test cases, and make comment style consistent.

There is no code changes in this CL, just a copy/paste and some
wordsmithing.

Change-Id: I418e8aed5ab997fad4214e8049287cac4bce8bf6
Reviewed-on: https://go-review.googlesource.com/11274
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

golang/image