Bug 750625 - Fix Coverity (11061) Resource leak
    
    https://bugzilla.redhat.com/show_bug.cgi?id=750625
    
    slapd/mapping_tree.c (mapping_tree_entry_add)
    
    Bug Description: Variable "subtree" going out of scope leaks
    the storage it points to.
    Slapi_DN subtree leaks when defbackend_get_backend returns NULL.
    
    Fix Description: Free "subtree" before returning.