* fork.cc (fork): Eliminate superfluous call to getuid().

    * fork.cc (fork): Eliminate superfluous call to getuid().
        * security.h: New define `NO_SID'. Remove declarations of functions
        moved to methods into class cygsid.
        (class cygsid): Declare new methods `getfromstr', `get_sid',
        `getfrompw', `getfromgr', `get_rid', `get_uid', `get_gid', `string'
        and new constructors and operators =, == and !=.
        Declare new global cygsids `well_known_XXX_sid' substituting the
        corresponding `get_XXX_sid' functions. Remove declarations of
        these functions.
        * sec_helper.cc (well_known_admin_sid): New global variable.
        (well_known_system_sid): Ditto
        (well_known_creator_owner_sid): Ditto
        (well_known_world_sid): Ditto
        (cygsid::string): New method, substituting `convert_sid_to_string_sid'.
        (cygsid::get_sid): New method, substituting `get_sid'.
        (cygsid::getfromstr): New method, substituting
        `convert_string_sid_to_sid'.
        (cygsid::getfrompw): New method, substituting `get_pw_sid'.
        (cygsid::getfromgr): New method, substituting `get_gr_sid'.
        (cygsid::get_id): New method, substituting `get_id_from_sid'.
        (get_admin_sid): Eliminated.
        (get_system_sid): Ditto.
        (get_creator_owner_sid): Ditto.
        (get_world_sid): Ditto.
        * grp.cc: Use new cygsid methods and well known sids throughout.
        * registry.cc: Ditto.
        * sec_acl.cc: Ditto.
        * security.cc: Ditto.
        * shared.cc: Ditto.
        * syscalls.cc (seteuid): Ditto. Eliminate redundant conditional.
        * uinfo.cc (internal_getlogin): Ditto.
        * spawn.cc (spawn_guts) Revert previous patch.