ITS#5408 part 8 - Rewrite search API, structs bvlist/enumCookie/ldif_tool.

r_enum_search() -> ldif_send_entry() + ldif_readdir() + ldif_search_entry().
enum_tree() -> search_tree().  fullpath() -> fullpath_alloc() + FILL_PATH().
No functionality change except catching malloc and opendir() errors.