git-daemon-run: default server location contradicts the FHS

[Allan Caffee]

I noticed that the package git-daemon-run by default expects the repositories
it serves to be located in /var/cache/git.  This behavior contradicts the FHS
which states

       /var/cache is intended for cached data from applications. Such data is
       locally generated as a result of time-consuming I/O or calculation.
       The application must be able to regenerate or restore the data.
       [...]
       The application must always be able to recover from manual deletion of
       these files (generally because of a disk space shortage).

This sets people up to have their entire repositories deleted by an admin
looking to free disk space.  :( I realize that the README.Debian for this
package suggests that the repositories themselves should be symbolic links, but
it seems dangerous all the same.  I think we should change the default to
/srv/git.

       Allan