#50 libdk should avoid using libsm's sm_strlcat & sm_strlcpy

[Fredrik Pettai]

To build third-party applications with domainkeys support (from libdk), you need to use -lsm (sendmails libsm) for sm_strlcat and sm_strlcpy that are
used in libdk.
Then possible, (lib)dk should utilize the OS native strlcat and strlcpy instead.