Modify all tests to use the Test::Simple lib

All tests now use the Test::Simple library.  We keep the distinction between
pl (pure perl) and plt (perl + Test::Simple) in case someone wants to write a
perl tests without this lib.

- t/pm/*: All tests now use the plt extension and the Test::Simple library.
- t/pm/CondStack.pl: Remove it as it was not well built and the test results
  were false.