Add a few missing headers.

Fixes build with gcc 4.3.2 on Debian.

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>

tools/atree/files.cpp

@@ -5,6 +5,8 @@
 #include <unistd.h>
 #include <dirent.h>
 #include <fnmatch.h>
+#include <string.h>
+#include <stdlib.h>
 
 static bool
 is_comment_line(const char* p)

tools/atree/fs.cpp

@@ -9,6 +9,7 @@
 #include <errno.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <string.h>
 #include <host/CopyFile.h>
 
 using namespace std;