### Please describe the problem.
I am trying to switch to direct mode with the git work tree in a different directory than default much like described in http://git-annex.branchable.com/forum/Detached_git_work_tree__63__/


### What steps will reproduce the problem?
- Create a new git repo with the GIT_WORK_TREE and GIT_DIR set.
- git annex init test
- git annex direct


### What version of git-annex are you using? On what operating system?
5.20141125 package in Debian unstable


### Please provide any additional information below.

[[!format sh """
+dbn@loaner:~/annex $ mkdir -p test/worktree
+dbn@loaner:~/annex $ cd test/
+dbn@loaner:~/annex/test $ git init
Initialized empty Git repository in /home/dbn/annex/test/.git/
+dbn@loaner:~/annex/test $ git annex init test
init test ok
(Recording state in git...)
+dbn@loaner:~/annex/test $ git annex direct --debug
commit  
[2014-12-08 03:05:45 PST] call: git ["--git-dir=/home/dbn/annex/test/.git","--work-tree=/home/dbn/annex/test/worktree","commit","-a","-m","commit before switching to direct mode"]
On branch master

Initial commit

nothing to commit
ok
[2014-12-08 03:05:45 PST] read: git ["--git-dir=/home/dbn/annex/test/.git","--work-tree=/home/dbn/annex/test/worktree","ls-files","--cached","-z","--","/home/dbn/annex/test/worktree"]
direct  [2014-12-08 03:05:45 PST] read: git ["--git-dir=/home/dbn/annex/test/.git","--work-tree=/home/dbn/annex/test/worktree","symbolic-ref","HEAD"]
[2014-12-08 03:05:45 PST] read: git ["--git-dir=/home/dbn/annex/test/.git","--work-tree=/home/dbn/annex/test/worktree","show-ref","--hash","refs/heads/master"]
[2014-12-08 03:05:45 PST] call: git ["--git-dir=/home/dbn/annex/test/.git","--work-tree=/home/dbn/annex/test/worktree","checkout","-q","-B","annex/direct/master"]
[2014-12-08 03:05:45 PST] call: git ["--git-dir=/home/dbn/annex/test/.git","--work-tree=/home/dbn/annex/test/worktree","config","core.bare","true"]
[2014-12-08 03:05:45 PST] read: git ["config","--null","--list"]
fatal: core.bare and core.worktree do not make sense

git-annex: user error (git ["config","--null","--list"] exited 128)
failed
git-annex: direct: 1 failed
"""]]
