* shared_info.h: Include security.h.
(open_shared): Add psa argument.
(user_shared_initialize): New declaration.
* security.h: Add _SECURITY_H guard.
(sec_user): Use sec_none in the no ntsec case.
* spawn.cc (spawn_guts): Remove call to load_registry_hive.
* syscalls (seteuid32): If warranted, call load_registry_hive,
user_shared_initialize and RegCloseKey(HKEY_CURRENT_USER).
* shared.cc (user_shared_initialize): New.
(open_shared): Add and use psa argument.
(memory_init): Move mount table initialization to
user_shared_initialize. Call it.