### Please describe the problem.

When commands that need gpg like `git annex copy` are run inside tmux, the GPG prompt does not show up and the user cannot give their password.

Running the same command outside tmux causes GPG to properly show its prompt

### What steps will reproduce the problem?

    $ tmux
    TMUX$ GIT_ANNEX_ROOT/runshell
    TMUX$ git annex copy --not -in remote --to remote

git-annex will show the name of the first filename but will get stuck soon after that, waiting for GPG.

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

git-annex 5.20140708-g8c9cc55c from the precompiled binaries, run inside tmux 1.6.

`tmux.conf` contains `set-option -g default-command $SHELL` (this means that a normal shell is spawned, not a login shell)

Ubuntu 12.04.4

[[!tag moreinfo]]

> [[done]]; apparently a local misconfiguration of some sort. --[[Joey]]
