[backend] publish: log execution of published hooks

Log which hook was executed for a published project to the publishers logfile.

src/backend/bs_publish

@@ -1834,6 +1834,7 @@ publishprog_done:
     }
   }
   if ($BSConfig::publishedhook && $BSConfig::publishedhook->{$publish_prp}) {
+    print "    calling published hook $BSConfig::publishedhook->{$publish_prp}\n";
     qsystem($BSConfig::publishedhook->{$publish_prp}, $prp, $extrep, @changed) && warn("    $BSConfig::publishedhook->{$publish_prp} failed: $?");
   }