Ticket 47792 - database plugins need a way to call betxn
     plugins
    
    Bug Description:  Database plugins like "chaining" register their
                      own add/mod/delete/modrdn functions.  These new
                      operation functions do not call the be/betxn plugins.
    
    Fix Description:  Created two new private functions to call the
                      pre & post be/betxn plugins.  Added these functions
                      to the chaining plugin.  Maybe in the future these
                      functions will be made public(slapi api).
    
                      Also fixed a harmless startup/initialization
                      memory leak.
    
    https://fedorahosted.org/389/ticket/47792
    
    Jenkins: passed.
    Valgrind: passed.
    
    Reviewed by: rmeggins & lkrispenz (Thanks!!)
    
    (cherry picked from commit 9929b439b766e807ad77285e3b3babb514dde897)