Fixed bug in lookup user mapping

If a local user was located in a multi-value ldap attribute,
it was not found by spmfilter.
Version 0.6.5
Fixed bug with NULL value headers.
Fixed bug in smf_message_write_skip_header()

smf_message_write_skip_header() returned an error
code if a message had no body. Now 0 will be returned.
Version 0.6.6