Switch to using SIDs in make_private_security_descriptor().

Daniel Meidlinger reports that at least one Windows machine which is
not obviously otherwise misconfigured will respond to our
SetEntriesInAcl call with odd errors like ERROR_NONE_MAPPED or
ERROR_TRUSTED_RELATIONSHIP_FAILURE. This is apparently to do with
failure to convert the names "EVERYONE" and "CURRENT_USER" used in the
ACL specification to SIDs. (Or perhaps only one of them is the problem
- I didn't investigate in that direction.)

If we instead construct a fully SID-based ACL, using the well-known
world SID in place of EVERYONE and calling our existing get_user_sid
routine in place of CURRENT_USER, he reports that the problem goes
away, so let's do that instead.

While I'm here, I've slightly simplified the function prototype of
make_private_security_descriptor(), by turning 'networksid' into an
internal static that we can reuse in subsequent calls once we've set
it up. (Mostly because I didn't fancy adding another two pointless
parameters at every call site for the two new SIDs.)

[originally from svn r10096]

windows/winsecur.h

@@ -50,15 +50,13 @@ PSID get_user_sid(void);
  * servers, i.e. allowing access only to the current user id and also
  * only local (i.e. not over SMB) connections.
  *
- * If this function returns TRUE, then 'psd', 'networksid' and 'acl'
- * will all have been filled in with memory allocated using LocalAlloc
- * (and hence must be freed later using LocalFree). If it returns
- * FALSE, then instead 'error' has been filled with a dynamically
- * allocated error message.
+ * If this function returns TRUE, then 'psd' and 'acl' will have been
+ * filled in with memory allocated using LocalAlloc (and hence must be
+ * freed later using LocalFree). If it returns FALSE, then instead
+ * 'error' has been filled with a dynamically allocated error message.
  */
 int make_private_security_descriptor(DWORD permissions,
                                      PSECURITY_DESCRIPTOR *psd,
-                                     PSID *networksid,
                                      PACL *acl,
                                      char **error);