### Please describe the problem.

Git annex cannot add files that are marked read-only

### What steps will reproduce the problem?

    $ echo "This should not be modified" > read_only_file.txt
    $ chmod 400 read_only_file.txt
    $ git annex add .
    add read_only_file.txt (checksum...) 
    git-annex: read_only_file.txt: removeLink: permission denied (Permission denied)
    failed

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

    git-annex version: 4.20131106
    build flags: Assistant Webapp Pairing Testsuite S3 WebDAV Inotify DBus XMPP Feeds Quvi TDFA CryptoHash
    key/value backends: SHA256E SHA1E SHA512E SHA224E SHA384E SKEIN256E SKEIN512E SHA256 SHA1 SHA512 SHA224 SHA384 SKEIN256 SKEIN512 WORM URL
    remote types: git gcrypt S3 bup directory rsync web webdav glacier hook
    local repository version: 3
    default repository version: 3
    supported repository versions: 3 4
    upgrade supported from repository versions: 0 1 2

    git version 1.8.4.3

