Ignore untranslated texts in check_po.pl

check_po.pl lists lots of false positives saying that
    msgstr ""
does not have the (h)otkey translated.

This patch whitelists those untranslated strings.

I also tested (by manually "breaking" a translation) that missing
hotkeys still get noticed.

This bug probably exists since forever, therefore I propose this patch
for 2.9..trunk. (OTOH, nobody noticed it, so maybe trunk is enough ;-)

Note: I still get a few false positives for ru.po (no idea why, similar
texts in the other languages don't cause this) - ideas and fixes welcome.

utils/check_po.pl

@@ -38,7 +38,7 @@ sub check_po_for_shortcuts {
               $msgid = $_;
             } 
             if ( /^.*msgstr*/ && $looking_for_msgstr ) {
-                unless (/^.*msgstr.*\(\w{1}?\)*/) {
+                unless (/^.*msgstr.*\(\w{1}?\)*/ or /^msgstr ""$/) {
                     $errors->{$filename}{$line} =  {
                                              "msgid" => $msgid,
                                              "msgstr" => $_,