Take care about the RR entries when computing the size, and cache it.

When computing the size of the directory structures, take care about the size
taken by the RR/SUSP fields. Also, cache that size, otherwise we need to do
this computation several times and it is ugly, because the CE entries need to 
know where the Continuation Area will be stored.

src/ecma119_tree.h

@@ -30,6 +30,15 @@ struct ecma119_dir_info {
     size_t nchildren;
     Ecma119Node **children;
     
+    /* 
+     * Size of the dir, i.e., sum of the lengths of all directory records.
+     * It is computed by calc_dir_size() [ecma119.c].
+     * Note that this don't include the length of any SUSP Continuation
+     * Area needed by the dir, but it includes the size of the SUSP entries
+     * than fit in the directory records System Use Field.
+     */ 
+    size_t len;
+    
     /** 
      * Real parent if the dir has been reallocated. NULL otherwise.
      */