### Please describe the problem.
I am importing a lot of old documents into my annex.  Some of these old files apparently have newlines in their filename.  A run of `git annex import` aborts when it encounters such a file; the file is moved to the annex, but it is left unstaged.

### What steps will reproduce the problem?
[[!format sh """
bram@durian% mkdir annex
bram@durian% cd annex
bram@durian% git init
Initialized empty Git repository in /home/bram/tmp/t/annex/.git/
bram@durian% git annex init
init  ok
(Recording state in git...)
bram@durian% echo foo > ../$'foo\nbar'
bram@durian% ls -lb ..
total 8
drwxr-xr-x 3 bram bram 4096 Jul 26 18:20 annex/
-rw-r--r-- 1 bram bram    4 Jul 26 18:20 foo\nbar
bram@durian% git annex import ../foo$'\n'bar
import foo
bar git-annex: unknown response from git cat-file ("HEAD:./foo missing","HEAD:./foo\nbar")
bram@durian% ls -lb
total 4
-r--r--r-- 2 bram bram 4 Jul 26 18:20 foo\nbar
bram@durian% git status
On branch master

Initial commit

Untracked files:
  (use "git add <file>..." to include in what will be committed)

	"foo\nbar"

nothing added to commit but untracked files present (use "git add" to track)
bram@durian% cat $'foo\nbar'
foo
"""]]


### What version of git-annex are you using? On what operating system?
    Debian unstable
    git-annex version: 5.20140717
    git version 2.0.1
    Linux durian 3.14-1-amd64 #1 SMP Debian 3.14.9-1 (2014-06-30) x86_64 GNU/Linux

[[!tag confirmed git-bug]]
[[!title git limitations prevent using git-annex on filenames containing newlines]]