Bug 15080 - ./translate tool should tell if xgettext executable is missing

Bug 15080 - ./translate tool should tell if xgettext executable is missing

Just upgraded our Koha container to 14.04 and noticing the
misc/translator/translate doesn't work.  This is because of a missing
package gettext.

This patch makes ./translate die with a helpful suggestion to install
gettext if xgettext-program is missing.

Signed-off-by: Frederic Demians <f.demians@tamil.fr>
  I can reproduce the bug by desinstalling 'gettext' package on a Debian
  box. I confirm that without this patch, 'translate' command fails
  miserably. Suggesting to install gettext package is welcomed.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jesse Weaver <jweaver@bywatersolutions.com>