- new ptvcursor subtrees management functions :

- new ptvcursor subtrees management functions :
  * ptvcursor_push_subtree(), ptvcursor_pop_subtree() for pushing/popping
    subtrees. Multiple levels of subtrees (256 max.), allocation per 8 levels.
  * Two new functions creating an item in the tree and pushing a subtree at the
    same time. These two functions accept an undefined length
    (SUBTREE_UNDEFINED_LENGTH). The length of the item is set at the next pop.
        1) ptvcursor_add_with_subtree
	2) ptvcursor_add_text_with_subtree
- get rid of potential memory leaks with g_new in ptvcursor_new().

- Documentation of the new ptvcursor functions in README.developer

svn path=/trunk/; revision=21276