### Please describe the problem.

Trying to do a "git-annex reinit" on Android (sdcard) fails with an error about failing to set a permission. I tried "git-annex init" as well, and that gave the same error.

### What steps will reproduce the problem?

```
$ git clone ssh://user@host/Westerley-Board.git
⋮
$ cd Westerley-Board/
$ git-annex reinit bc11f6b5-753c-4aeb-88e2-0c2f582e9901
reinit bc11f6b5-753c-4aeb-88e2-0c2f582e9901 warning: Cannot protect .git/config on this file system - do not store sensitive information here.

  Detected a filesystem without fifo support.

  Disabling ssh connection caching.
warning: Cannot protect .git/config on this file system - do not store sensitive information here.

  Detected a crippled filesystem.
warning: Cannot protect .git/config on this file system - do not store sensitive information here.
(merging origin/git-annex into git-annex...)
(recording state in git...)
warning: Cannot protect .git/config on this file system - do not store sensitive information here.
warning: Cannot protect .git/config on this file system - do not store sensitive information here.
warning: Cannot protect .git/config on this file system - do not store sensitive information here.
(scanning for unlocked files...)

git-annex: .git/annex/keys.tmp/db: setFileMode: permission denied (Operation not permitted)
failed
git-annex: reinit: 1 failed
```

`git-annex init` fails with the same error.

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

OS: Android, on a Amazon Fire Tablet 10. Installed in Termux via the new method (the script); edited the script to tell it to use armel on armv8l. (Supposedly a 64-bit chip, but the Android build is apparently 32-bit).

git-annex version: 7.20190504-g5638ae968

### Please provide any additional information below.


### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Yes! I have been using it on this tablet for a while, using the previous Android install steps. That was always a bit buggy, was hoping to upgrade to the new method. I also use git-annex on a bunch of Debian boxes, where it is wonderful. Have somewhere between ½ and ¾ TB data in git-annex, in enough repositories and copied to enough machines that I'd have to sit down and think about it to count them all.
