### Please describe the problem.
Unable to use webapp after creating annex. Error `The file /annex/webapp.html does not exist.` is shown.


### What steps will reproduce the problem?
Create annex, either using webapp or command line. Kill the webapp and attempt to relaunch.


### What version of git-annex are you using? On what operating system?
git-annex version: 5.20150205

OS X Version: 10.10.3 (14D136)

Installed using homebrew

### Please provide any additional information below.


It appears that git-annex is using an absolute path, rather than a relative path pointing to `.git/annex/webapp.html`.
Manually opening the file at `.git/annex/webapp.html` does however show the correct web interface.

[[!format sh """
 git-annex webapp
Launching web browser on file://.git/annex/webapp.html
The file /annex/webapp.html does not exist.
"""]]

> This is an old version of git-annex and there was known breakage around
> that time from the relative path conversion, since fixed, which IIRC
> would manifest this way. [[done]] --[[Joey]]
