Adds the specified member to the group.

  Adds the specified member to the group.
Returns: true if the member was successfully added, false if the principal was already a member.
Parameters:
- user - the principal to add to this group.

  Returns true if the passed principal is a member of the group.

  Returns true if the passed principal is a member of the group.
This method does a recursive search, so if a principal belongs to a
group which is a member of this group, true is returned.
Returns: true if the principal is a member of this group, false otherwise.
Parameters:
- member - the principal whose membership is to be checked.

  Returns an enumeration of the members in the group.

  Returns an enumeration of the members in the group.
The returned objects can be instances of either Principal
or Group (which is a subclass of Principal).
Returns: an enumeration of the group members.

  Removes the specified member from the group.

  Removes the specified member from the group.
Returns: true if the principal was removed, or false if the principal was not a member.
Parameters:
- user - the principal to remove from this group.