Add missing string.h that would otherwise soon break the build.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@26453 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/add-ons/kernel/drivers/tty/master.cpp

@@ -7,6 +7,7 @@
 #include "tty_private.h"
 
 #include <stdlib.h>
+#include <string.h>
 #include <util/AutoLock.h>
 
 

src/add-ons/kernel/drivers/tty/slave.cpp

@@ -5,6 +5,7 @@
 
 
 #include <stdlib.h>
+#include <string.h>
 
 #include <util/AutoLock.h>
 

src/add-ons/kernel/file_systems/ext2/Volume.cpp

@@ -12,6 +12,7 @@
 #include <new>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include <fs_cache.h>
 #include <fs_volume.h>