rasterlib: add missing header

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@52566 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/raster/xdr.c

@@ -1,5 +1,6 @@
 
 #include <stdlib.h>
+#include <string.h>
 #include <grass/raster.h>
 
 #include "R.h"