dabbad: open pid file as write only.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabbad: add pid file doxygen header.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
Merge pull request #13 from eroullit/pidfile-wronly

Give dabbad write only permissions to create PID file