Added support for adding tab completions to any command with out a build in

Added support for adding tab completions to any command with out a build in
completion function.
add the folowing line to allow tab completion on element set name f2locations
to the elements command

  register_tab elements f2locations

som small clean up of the tabcompletions added completion on filenames to
the set_apdufile set_marcdump . and ! commands
now uses strncasecmp when findding stuff to complete on. eg
format xml "tabcomplets to" format XML

Extended authentication command to allow 2 arguments and send userid and
password in the Z_IdAuthentication_idPass structure