For seamless cube maps the pitch (in pixels) differs from the width,
due to the border.

Also renamed identicalFormats() to identicalBuffers() since much more
than the format is compared to determine if the buffers should be
identical.

Bug swiftshader:45

Change-Id: I295557b2cb039615a624c106be3e74588463b102
Reviewed-on: https://swiftshader-review.googlesource.com/19668Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>