Vlib: dox: note about freeing

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@52319 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/vector/Vlib/cats.c

@@ -30,6 +30,8 @@ struct line_cats *Vect__new_cats_struct(void);
 
    This structure is used for reading and writing vector cats. The
    library routines handle all memory allocation.
+   
+   To free allocated memory call Vect_destroy_cats_struct().
 
    \return struct line_cats *
    \return NULL on error

lib/vector/Vlib/line.c

@@ -35,6 +35,8 @@ struct line_pnts *Vect__new_line_struct(void);
   polygons.  The library routines handle all memory allocation.  If 3
   lines in memory are needed at the same time, then simply 3 line_pnts
   structures have to be used.
+  
+  To free allocated memory call Vect_destroy_line_struct().
 
   Calls G_fatal_error() on error.