image/draw: have Transform take a f64.Aff3 instead of a *f64.Aff3.

It's more args (in terms of bytes), but fewer allocations (Transformer
is an interface). Either way, it's not really that big of a deal, but
the value instead of the pointer seems conceptually more correct.

Change-Id: Ibea76da17cbda0d9633110fd56044b4e2c690e81
Reviewed-on: https://go-review.googlesource.com/12669
Reviewed-by: Rob Pike <r@golang.org>
5 files changed