* autoload.cc: Add LoadDLLinitfunc for secur32.dll.

    * autoload.cc: Add LoadDLLinitfunc for secur32.dll.
        Add LoadDLLfuncEx statements for AllocateLocallyUniqueId@4,
        DuplicateTokenEx@24, LsaNtStatusToWinError@4,
        LsaDeregisterLogonProcess@4, LsaFreeReturnBuffer@4,
        LsaLogonUser@56, LsaLookupAuthenticationPackage@12,
        LsaRegisterLogonProcess@12,
        * environ.cc: Add extern declaration for `subauth_id'.
        (subauth_id_init): New function for setting `subauth_id'.
        (struct parse_thing): Add entry for `subauth_id'.
        * fork.cc (fork_parent): Call `RevertToSelf' and
        `ImpersonateLoggedOnUser' instead of `seteuid'.
        * security.cc: Define global variable `subauth_id'.
        (extract_nt_dom_user): New function.
        (cygwin_logon_user): Call `extract_nt_dom_user' now.
        (str2lsa): New static function.
        (str2buf2lsa): Ditto.
        (str2buf2uni): Ditto.
        (subauth): Ditto.
        * security.h: Add prototype for `subauth'.
        * spawn.cc (spawn_guts): Use cygheap->user.token only if impersonated.
        Use `cygsid' type. Remove impersonation before allowing access to
        workstation/desktop to everyone. Call `RevertToSelf' and
        `ImpersonateLoggedOnUser' instead of `seteuid'.
        * syscalls.cc (seteuid): Rearranged to allow using subauthentication
        to retrieve user tokens when needed.