573896 - initializing subtree with invalid syntax crashes ns-slapd
    
    https://bugzilla.redhat.com/show_bug.cgi?id=573896
    
    Description: When an import is executed using a task mechanism,
    slapi_task_log_notice is called for logging, where task_log field
    points the memory storing the log messages.  If multiple log
    messages were logged by multiple worker threads simultaneously,
    there was a chance that the address of the log message was switched
    by realloc while the other threads were accessing the old address.
    This patch introduces task_log_lock per task to protect task_log.
    Note: slapi_ch_malloc and its friends never return NULL. They rather
    exits.  Thus, to avoid the confusion which may look leaking the
    lock, I eliminated 2 error returns from slapi_task_log_notice.