dabbad: give group pidfile read access.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabbad: set 660 perm to unix socket file.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
cmake: add 'adduser' to the list of dependencies.

'adduser' is only needed to create a low-privilege dabba user/group to run
the daemon on.
Users needing access to it can be registered in the dabba group.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
init.d: make sure /var/run/dabba is present.

Making sure this directory belongs to the proper user/group insures
proper permissions for the socket, pid files created in it.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>