i18n: add--interactive: mark patch prompt for translation

i18n: add--interactive: mark patch prompt for translation

Mark prompt message assembled in place for translation, unfolding each
use case for each entry in the %patch_modes hash table.

Previously, this script relied on whether $patch_mode was set to run the
command patch_update_cmd() or show status and loop the main loop. Now,
it uses $cmd to indicate we must run patch_update_cmd() and $patch_mode
is used to tell which flavor of the %patch_modes are we on.  This is
introduced in order to be able to mark and unfold the message prompt
knowing in which context we are.

The tracking of context was done previously by point %patch_mode_flavour
hash table to the correct entry of %patch_modes, focusing only on value
of %patch_modes. Now, we are also interested in the key ('staged',
'stash', 'checkout_head', ...).

Signed-off-by: Vasco Almeida <vascomalmeida@sapo.pt>
Signed-off-by: Junio C Hamano <gitster@pobox.com>