Ticket 20 - Allow automember to work on entries that have already been added
    
    Bug Description:  If the server can not open a ldif for reading(mapping task), an
                      incorrect error and file name is returned.
    
    Fix Description:  Report the correct file name, and correctly grab the OS error/string.
                      Also made slapd_pr_strerr() and slapd_system_strerr() public, so I
                      refactored the function names to be "slapi_" - so a lot of files are
                      touched but the main change for this ticket is still in automember.c
    
    https://fedorahosted.org/389/ticket/20
    
    Reviewed by: richm(Thanks)
    (cherry picked from commit bf2bfaab8e61f335442e4341ff33521a822bd830)