Fix builds with external talloc

Make sure we do not reference our internal talloc directly.
Let configure define what talloc.h file to use so that builds that use an
extrenal talloc do not include 2 different versions of the talloc header.

lib/util/talloc_stack.h

@@ -35,7 +35,7 @@
 #ifndef _TALLOC_STACK_H
 #define _TALLOC_STACK_H
 
-#include "../talloc/talloc.h"
+#include "talloc.h"
 
 /*
  * Create a new talloc stack frame.

nsswitch/libwbclient/wbclient.c

@@ -23,8 +23,8 @@
 /* Required Headers */
 
 #include "replace.h"
-#include "lib/talloc/talloc.h"
-#include "lib/tevent/tevent.h"
+#include "talloc.h"
+#include "tevent.h"
 #include "libwbclient.h"
 
 /* From wb_common.c */

source3/include/includes.h

@@ -621,7 +621,7 @@ struct smb_iconv_convenience *lp_iconv_convenience(void *lp_ctx);
 #include "tdb.h"
 #include "util_tdb.h"
 
-#include "../talloc/talloc.h"
+#include "talloc.h"
 
 #include "event.h"
 #include "../lib/util/tevent_unix.h"