vlib: note that temporary vector maps are overwritten if they exist

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@55403 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/vector/Vlib/open.c

@@ -841,7 +841,8 @@ int Vect_open_new(struct Map_info *Map, const char *name, int with_z)
   \brief Create new temporary vector map
 
   Temporary vector maps are stored in the current mapset (directory
-  <tt>.tmp/<hostname>/vector</tt>).
+  <tt>.tmp/<hostname>/vector</tt>). If the map already exists, it is
+  overwritten.
 
   Temporary vector maps are automatically deleted when closing the map
   (see Vect_close() for details).