### Please describe the problem.

I added a google-cloud nearline special remote.  It worked great for about two weeks.  But now I cannot do any operations on the bucket; they all fail with 400s.

### What steps will reproduce the problem?

(I've XXX'ed out things that look like they might contain secrets.)

	$ AWS_ACCESS_KEY_ID=GOOGXXX AWS_SECRET_ACCESS_KEY=XXX git annex copy --to goog-cloud-nearline2 photos/raw-photos/2007/Birds\ at\ GovCo/ --debug --json --verbose
	[2016-11-02 10:09:43.617264] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","show-ref","git-annex"]
	[2016-11-02 10:09:43.628311] process done ExitSuccess
	[2016-11-02 10:09:43.62842] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","show-ref","--hash","refs/heads/git-annex"]
	[2016-11-02 10:09:43.638154] process done ExitSuccess
	[2016-11-02 10:09:43.639472] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch"]
	[2016-11-02 10:09:43.670284] read: git ["config","--null","--list"]
	[2016-11-02 10:09:43.684014] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","ls-files","--cached","-z","--","photos/raw-photos/2007/Birds at GovCo/"]
	copy photos/raw-photos/2007/Birds at GovCo/IMG_4186.dng (checking goog-cloud-nearline2...) [2016-11-02 10:09:43.845838] String to sign: "HEAD\n\n\nWed,  2 Nov 2016 17:09:43 GMT\n/jlebar-annex-nearline2/GPGHMACSHA1--07b92ba4ec937b88911ce8128974ba449382113d"
	[2016-11-02 10:09:43.845906] Host: "jlebar-annex-nearline2.storage.googleapis.com"
	[2016-11-02 10:09:43.845938] Path: "/GPGHMACSHA1--07b92ba4ec937b88911ce8128974ba449382113d"
	[2016-11-02 10:09:43.845966] Query string: ""
	[2016-11-02 10:09:43.954556] Response status: Status {statusCode = 400, statusMessage = "Bad Request"}
	[2016-11-02 10:09:43.954689] Response header 'X-GUploader-UploadID': 'XXX'
	[2016-11-02 10:09:43.954818] Response header 'Content-Type': 'application/xml; charset=UTF-8'
	[2016-11-02 10:09:43.954893] Response header 'Content-Length': '178'
	[2016-11-02 10:09:43.95498] Response header 'Date': 'Wed, 02 Nov 2016 17:09:41 GMT'
	[2016-11-02 10:09:43.955017] Response header 'Expires': 'Wed, 02 Nov 2016 17:09:41 GMT'
	[2016-11-02 10:09:43.955047] Response header 'Cache-Control': 'private, max-age=0'
	[2016-11-02 10:09:43.955143] Response header 'Server': 'UploadServer'
	[2016-11-02 10:09:43.95518] Response metadata: S3: request ID=<none>, x-amz-id-2=<none>
	(StatusCodeException (Status {statusCode = 400, statusMessage = "Bad Request"}) [("X-GUploader-UploadID","XXX"),("Content-Type","application/xml; charset=UTF-8"),("Content-Length","178"),("Date","Wed, 02 Nov 2016 17:09:41 GMT"),("Expires","Wed, 02 Nov 2016 17:09:41 GMT"),("Cache-Control","private, max-age=0"),("Server","UploadServer")] (CJ {expose = []})) failed
	git-annex: copy: 1 failed
	CallStack (from HasCallStack):
	  error, called at ./CmdLine/Action.hs:41:28 in main:CmdLine.Action

### What version of git-annex are you using? On what operating system?

	$ git annex version
	git-annex version: 6.20160923
	build flags: Assistant Webapp Pairing Testsuite S3(multipartupload)(storageclasses) WebDAV FsEvents XMPP ConcurrentOutput TorrentParser MagicMime Feeds Quvi
	key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 SHA1E SHA1 MD5E MD5 WORM URL
	remote types: git gcrypt S3 bup directory rsync web bittorrent webdav tahoe glacier ddar hook external
	local repository version: 6
	supported repository versions: 5 6
	upgrade supported from repository versions: 0 1 2 3 4 5
	operating system: darwin x86_64

### Please provide any additional information below.

As I read their docs, GCS should be sending back a more helpful error message
in the body of the response:
https://cloud.google.com/storage/docs/xml-api/reference-status.  I tried to
figure out how to get git annex to print that out, but...did you know git annex
is a nontrivial Haskell program?  :)

If we could get git annex to print out the body of the response and there is in
fact an error message in there, I expect the reason for this error would be
obvious.  Or if we could get git annex to do a "dry run" and print the HTTP
requeset it *would have* made, I could probably run it in curl and get the
response that way.

(I actually considered setting up wireshark to capture the response, but I'd
have to set up an HTTPS MITM...)

I cannot figure out what made this stop working all of a sudden.  I don't think it was a git annex version update, and I checked remotes.log, and this remote's metadata hasn't changed.  (The line for this remote has been updated a few times, but afaict only the timestamp changed.)

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

It was working so great up until it wasn't -- I was very happy.  Thank you
for all your work on this software; there is nothing like it.
