### Please describe the problem.

Initially reported in [heudiconv](https://github.com/nipy/heudiconv/pull/259).  I am not yet sure what is going on, but git-annex (tried "bleeding edge" from a few days back too) seems to believe being unable to get .git/config file, while I do not see any request being logged on the server side, and `curl` gets it just ok.

To reproduce you can use ```docker run -it --rm --entrypoint bash nipy/heudiconv:latest -c "cd /tmp/ && rm -rf /tmp/MEEPI3; git clone http://datasets-tests.datalad.org/dicoms/velasco/MEEPI/.git MEEPI3 && cd MEEPI3 && git annex info --debug; echo -e '\n\nCURL:'; curl http://datasets-tests.datalad.org/dicoms/velasco/MEEPI/.git/config"```


<details>
<summary>A sample docker run</summary>

[[!format sh """
docker run -it --rm --entrypoint bash nipy/heudiconv:latest -c "cd /tmp/ && rm -rf /tmp/MEEPI3; git clone http://datasets-tests.datalad.org/dicoms/velasco/MEEPI/.git MEEPI3 && cd MEEPI3 && git annex info --debug; echo -e '\n\nCURL:'; curl http://datasets-tests.datalad.org/dicoms/velasco/MEEPI/.git/config"
...
[2018-11-12 17:58:02.246908731] Request {
  host                 = "datasets-tests.datalad.org"
  port                 = 80
  secure               = False
  requestHeaders       = [("Range","bytes=0-"),("Accept-Encoding","identity"),("User-Agent","git-annex/6.20181011+git124-g94aa0e2f6-1~ndall+1")]
  path                 = "/dicoms/velasco/MEEPI/.git/config"
  queryString          = ""
  method               = "GET"
  proxy                = Nothing
  rawBody              = False
  redirectCount        = 10
  responseTimeout      = ResponseTimeoutDefault
  requestVersion       = HTTP/1.1
}


  Remote origin not usable by git-annex; setting annex-ignore
[2018-11-12 17:58:02.247631556] call: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","config","remote.origin.annex-ignore","true"]
[2018-11-12 17:58:02.249993683] process done ExitSuccess
[2018-11-12 17:58:02.250056119] read: git ["config","--null","--list"]
[2018-11-12 17:58:02.252212701] process done ExitSuccess
repository mode: indirect
trusted repositories: 0
semitrusted repositories: 6
	00000000-0000-0000-0000-000000000001 -- web
 	00000000-0000-0000-0000-000000000002 -- bittorrent
 	41bc6812-269a-47af-a7c9-ba2d30e55642 -- yoh@smaug:/mnt/btrfs/datasets/datalad/crawl/dicoms/velasco/MEEPI
 	757a81e7-f905-4796-9941-a2772ec190b6 -- yoh@falkor:/srv/datasets.datalad.org/www/dicoms/velasco/MEEPI
 	c04eb54b-4b4e-5755-8436-866b043170fa -- datalad-archives
 	ffa6417c-5511-4b43-a67a-036dd57ab974 -- root@d9efe0626d93:/tmp/MEEPI3 [here]
untrusted repositories: 0
transfers in progress: none
available local disk space: 12.08 gigabytes (+1 megabyte reserved)
local annex keys: 0
local annex size: 0 bytes
annexed files in working tree: [2018-11-12 17:58:02.253291443] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","ls-files","--cached","--others","-z","--","."]
[2018-11-12 17:58:02.255650007] process done ExitSuccess
3
size of annexed files in working tree: 5.87 megabytes
bloom filter size: 32 mebibytes (0% full)
backend usage: 
	MD5E: 3
[2018-11-12 17:58:02.256351183] process done ExitSuccess
[2018-11-12 17:58:02.256558475] process done ExitSuccess
[2018-11-12 17:58:02.256945107] process done ExitSuccess


CURL:
[core]
	repositoryformatversion = 0
	filemode = true
	bare = false
	logallrefupdates = true
	sharedrepository = 2
[receive]
	denyNonFastforwards = true
	denyCurrentBranch = updateInstead
[annex]
	uuid = 757a81e7-f905-4796-9941-a2772ec190b6
	version = 5


$> docker run -it --rm --entrypoint bash nipy/heudiconv:latest -c "git annex version | head -n1"
git-annex version: 6.20181011+git124-g94aa0e2f6-1~ndall+1 
"""]]

</details>



[[!meta author=yoh]]
[[!tag projects/repronim]]

> [[done]]; git-annex displays a good error message and the dependency is
> there. --[[Joey]]
