add ldap_strdup and eliminate strdup in libldap

libraries/libldap/Makefile.in

libraries/libldap/cldap.c

libraries/libldap/disptmpl.c

libraries/libldap/dsparse.c

libraries/libldap/friendly.c

libraries/libldap/getdn.c

libraries/libldap/getdxbyname.c

libraries/libldap/getfilter.c

libraries/libldap/init.c

libraries/libldap/ldap-int.h

libraries/libldap/open.c

libraries/libldap/options.c

libraries/libldap/os-ip.c

libraries/libldap/request.c

libraries/libldap/search.c

libraries/libldap/test.c

libraries/libldap/ufn.c

libraries/libldap/url.c