Testsuite: Fix calls to die to always include line numbers ...

'die' actually taking two parameters seems to be a little-known fact.

Fix some tests that were using installed DUB instead of built ones ...

Those tests were not actually testing the built dub,
but whatever was installed on the machine (or in the path) instead.

Update test/help.sh ...

Co-Authored-By: Jan Jurzitza <gh@webfreak.org>

Add bash script to tests the help command