[IMP] gen_translation: report missing msgcat + minor cleanup
[IMP] gen_translation: report missing msgcat + minor cleanup

- exit if msgcat command is missing
- use consistent command substitution style
- pass --force-po to msgcat to avoid spurious error messages in the subsequent mv call

havt/openerp-web,havt/openerp-web,akretion/openerp-web,akretion/openerp-web,akretion/openerp-web,havt/openerp-web,havt/openerp-web,havt/openerp-web