We now always write the "optional" streaming data descriptor
signature, which turns out to be required for OS X.
Also, handle reading the data descriptor with or without the
signature, per the spec's recommendation. Fix data descriptor
reading bugs found in the process.
Fixes#3252
R=golang-dev, alex.brainman, nigeltao, rsc
CC=golang-dev
https://golang.org/cl/5787062
This was an implementation detail that snuck into the public interface.
*Writer.Create gives you an io.Writer, the *Writer itself was never
meant to be written to.
R=golang-dev, dsymonds, r
CC=golang-dev
https://golang.org/cl/5654076
(*Writer, error) if they take a compression level, and *Writer otherwise.
Rename gzip's Compressor and Decompressor to Writer and Reader, similar to
flate and zlib.
Clarify commentary when writing gzip metadata that is not representable
as Latin-1, and fix io.EOF comment bug.
Also refactor gzip_test to be more straightforward.
Fixes#2839.
R=rsc, r, rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5639057
