### Please describe the problem.

I tried to add a Tahoe special remote as follows-
git annex initremote tahoe type=tahoe embedcreds=yes

However, this fails and gives me an error saying that tahoe create-client failed because .tahoe is not empty (even when .tahoe did not previously exist). It seems like git-annex is creating a .tahoe/git-annex directory (which is empty) and then trying to run tahoe create-client, which fails because the .tahoe directory was already created by git-annex.

### What steps will reproduce the problem?
1. Install tahoe and setup a plain git annex repo
2. export TAHOE_FURL=tahoe introducer url here
3. git annex initremote tahoe type=tahoe embedcreds=yes


### What version of git-annex are you using? On what operating system?
5.20141024~bpo70+1 on Tails 1.2.1 (Debian Wheezy 32-bit)


### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log
$ git annex initremote tahoe type=tahoe embedcreds=yes
 
initremote tahoe The base directory '/home/amnesia/.tahoe' is not empty.
To avoid clobbering anything, I am going to quit now.
Please use a different directory, or empty this one.
git-annex: tahoe create-client failed 

# End of transcript or log.
"""]]
