### Please describe the problem.

"git annex unlock" with an absolute path appears to do nothing.  Is this a feature or a bug?

### What steps will reproduce the problem?

[[!format sh """
> mkdir git_annex_test && cd git_annex_test/
> git init
> git annex init "Local copy"
> touch foo.txt
> git annex add foo.txt
> git commit -m "Checkin"
> git annex unlock foo.txt    (correct behavior)
> git annex lock --force foo.txt
> git annex unlock /absolute/path/to/git_annex_test/foo.txt    (appears to do nothing)
"""]]

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

Ubuntu 14.04.02 with git-annex from repo:

[[!format sh """
> git annex --version
git-annex version: 5.20140412ubuntu1
build flags: Assistant Webapp Webapp-secure Pairing Testsuite S3 WebDAV Inotify DBus DesktopNotify XMPP DNS 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 tahoe glacier hook external
local repository version: 5
supported repository version: 5
upgrade supported from repository versions: 0 1 2 4
""" ]]