Allow unsetting daemonize and close_fds

As mentioned in a previous commit, this does two changes:
 - Make want_daemonize return a bool (false on failure, true on success)
 - Make both want_daemonize and want_close_all_fds take a "state"
   argument so the user can choose to unset those flags.

This commit also updates all occurences of those two functions and turns
the daemonize attribute from an int to a bool.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Update doxygen doc for previous change

Reported-by: James Hunt <james.hunt@ubuntu.com>
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>