Renaming test files according to their language (#3407)

test/tw-3109.test.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+. bash_tap_tw.sh
+
+task add emptyval
+task 1 done
+task 1 mod end: status:pending
+task_end=`task 1 info | grep ^End | sed -e 's/^End //' || true`
+echo "task_end: $task_end"
+
+# `task mod end:` should have deleted the end.
+[[ "$task_end" == "" ]]