Bug 4126 - Exit bulkmarcimport if -a and -b given

Bug 4126 - Exit bulkmarcimport if -a and -b given

Currently it is possible to spceify both --biblios and --authorities
as command line switches to bulkmarcimport.pl. This does not make sense
so we should exit early and explain that these switches are mutually
exclusive.

To test:
- Run one of these and check that there is no complaint about missing
  options:
  perl misc/migration_tools/bulkmarcimport.pl -a -b
  sudo koha-shell -c "perl misc/migration_tools/bulkmarcimport.pl -a -b"
  kohadev
- Observe that this displays the perldoc, but does not complain about
  mutually exclusive switches.
- Apply the patch
- Rerun the command(s) from earlier.
- Verify that the script is now halted and a small explanation given.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>