+tck testing for test skipping and fix in spec104 skipping regression

* spec104 must be skipped, and not fail for no given error publisher
* added verification that spec112 is SKIPPED as expected, for no err-pub
* missing skip exception in optionalActivePublisherTest

* We uncovered that the 104 spec validation would not be properly skipped due to an regression - this is now fixed. To avoid such problems in the future, optional tests are now covered with tests that check that they SKIP as expected.
use two catch clauses instead:
~~~java
} catch(SkipException se) {
  throw se;
} catch(Throwable ex) {
  …
}
~~~