Bug 11510: koha-translate usage message fixes

Bug 11510: koha-translate usage message fixes

The koha-translate's usage message has a couple of inconsistencies:

'--all' should be '--available'
and '--help' is missing from the usage examples.

Sponsored-by: Universidad Nacional de Cordoba
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described, tested using instructions on
http://wiki.koha-community.org/wiki/Testing_man_pages

Signed-off-by: Galen Charlton <gmc@esilibrary.com>