### Please describe the problem.

A readonly repository that I can add fine on the commandline (and sync content from) cannot be added through the webapp.

### What steps will reproduce the problem?

Say I have a readonly (owned by root) repository in `~/test/a` and I create a `~/test/b` (owned by my user). In the webapp, when to add `/home/anarcat/test/a` as a "local repository" (`Add another local repository`) to the `~/test/b` repo, it fails when i enter that path, with "Cannot write a repository there." I obviously can't sync content from there then.

This works on the commandline, although with warnings.

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

Version: 5.20140927 
Build flags: Assistant Webapp Webapp-secure Pairing Testsuite S3 WebDAV Inotify DBus DesktopNotify XMPP DNS Feeds Quvi TDFA CryptoHash

Debian Jessie.

### Please provide any additional information below.

Here's the transcript of the commandline equivalent:

~~~
anarcat@marcos:test$ git init a
Dépôt Git vide initialisé dans /home/anarcat/test/a/.git/
anarcat@marcos:test$ git init b
Dépôt Git vide initialisé dans /home/anarcat/test/b/.git/
anarcat@marcos:test$ cd a
anarcat@marcos:a$ git annex init
init  ok
(Recording state in git...)
anarcat@marcos:a$ echo hellow world > README
anarcat@marcos:a$ git annex add README
add README ok
(Recording state in git...)
anarcat@marcos:a$ git commit -m"test repo a"
[master (commit racine) 3ece2a1] test repo a
 1 file changed, 1 insertion(+)
 create mode 120000 README
anarcat@marcos:a$ cd ../ ^C
anarcat@marcos:a$ sudo chown -R root .
[sudo] password for anarcat:
Sorry, try again.
[sudo] password for anarcat:
anarcat@marcos:a$ cd ../b
anarcat@marcos:b$ git annex init
init  ok
(Recording state in git...)
anarcat@marcos:b$ git remote add a ../a
anarcat@marcos:b$ git annex sync a
commit  ok
pull a
warning: no common commits
remote: Décompte des objets: 13, fait.
remote: Compression des objets: 100% (9/9), fait.
remote: Total 13 (delta 1), reused 0 (delta 0)
Dépaquetage des objets: 100% (13/13), fait.
Depuis ../a
 * [nouvelle branche] git-annex  -> a/git-annex
 * [nouvelle branche] master     -> a/master


merge: refs/remotes/a/synced/master - not something we can merge
failed
(merging a/git-annex into git-annex...)
(Recording state in git...)
push a
Décompte des objets: 8, fait.
Delta compression using up to 2 threads.
Compression des objets: 100% (6/6), fait.
Écriture des objets: 100% (8/8), 819 bytes | 0 bytes/s, fait.
Total 8 (delta 1), reused 0 (delta 0)
remote: error: insufficient permission for adding an object to repository database objects
remote: fatal: failed to write object
error: unpack failed: unpack-objects abnormal exit
To ../a
 ! [remote rejected] git-annex -> synced/git-annex (unpacker error)
 ! [remote rejected] master -> synced/master (unpacker error)
error: impossible de pousser des références vers '../a'

  Pushing to a failed.

  (non-fast-forward problems can be solved by setting receive.denyNonFastforwards to false in the remote's git config)
failed
git-annex: sync: 2 failed
anarcat@marcos:b$ ls
README
anarcat@marcos:b$ git annex copy --from a
copy README (from a...) ok
(Recording state in git...)
anarcat@marcos:b$ ls -al
total 16K
drwxr-xr-x 3 anarcat anarcat 4096 oct.  20 15:36 .
drwxr-xr-x 4 anarcat anarcat 4096 oct.  20 15:35 ..
drwxr-xr-x 9 anarcat anarcat 4096 oct.  20 15:36 .git
lrwxrwxrwx 1 anarcat anarcat  180 oct.  20 15:36 README -> .git/annex/objects/wz/Zq/SHA256E-s13--8c083c6897455257dfbace7a9012d92ca8ebfb6e6ebe8acddc6dfa8fc81226ed/SHA256E-s13--8c083c6897455257dfbace7a9012d92ca8ebfb6e6ebe8acddc6dfa8fc81226ed
~~~

This is part of the [[todo/read-only_removable_drives/]] series. --[[anarcat]]
