directory before running rmtree on it. Closes:#796773.
* Do not call "warn" on failure of cleanup handler in END block
(since warn has been made fatal and aborts the cleanup chain).
+ * Print better error message (with `fail' rather than `die') if
+ `dgit clone' cannot create the destination directory.
+ * Properly substitute $changesfile in one of the `You can retry'
+ messages. Closes:#800078.
Test suite:
* When sbuild fails, do not crash due to sed not finding the log