Partially revert change from 2005-04-03, always running under an

impersonation token, which collides with Vista UAC.
	* cygheap.h (deimpersonate): revert to self instead of impersonating
	hProcImpToken.
	(reimpersonate): Only impersonate if setuid.
	* dcrt0.cc (dll_crt0_0): Don't initialize hProcImpToken here.
	(dll_crt0_1): Set privileges on hProcToken.
	* fork.cc (frok::child): Set privileges on hProcToken.  Close handle to
	hProcImpToken.
	* grp.cc (internal_getgroups): Use hProcToken instead of hProcImpToken.
	* security.cc (check_access): Create hProcImpToken on demand here.
	* security.h (set_process_privilege): Set privileges on hProcToken.
	(_push_thread_privilege): Use hProcToken instead of hProcImpToken.
	(pop_thread_privilege): If not setuid'ed, revert to self.
	* syscalls.cc (setegid32): Drop setting primary group on hProcImpToken.
	Close handle to hProcImpToken.
	* uinfo.cc (internal_getlogin): Ditto.
	* winsup.h (clear_procimptoken): New inline function.

winsup/cygwin/cygheap.h

@@ -182,14 +182,13 @@ public:
   void deimpersonate ()
   {
     if (issetuid ())
-      {
-	RevertToSelf ();
-	ImpersonateLoggedOnUser (hProcImpToken);
-      }
+      RevertToSelf ();
   }
   bool reimpersonate ()
   {
-    return ImpersonateLoggedOnUser (issetuid () ? token () : hProcImpToken);
+    if (issetuid ())
+      return ImpersonateLoggedOnUser (token ());
+    return true;
   }
   bool has_impersonation_tokens ()
     { return external_token != NO_IMPERSONATION