[Simpletest-support] SimpleFileLoader::selectRunnableTests($candidates) filters abstract classes

[Pavel S. <pac...@gm...>]

Guys, I committed a minor change to
SimpleFileLoader::selectRunnableTests() which makes it not only mark
abstract classes as ignored but filter them as well.

Actual abstract classes filtering is done in
SimpleFileLoader::createSuiteFromClasses(..), however in our tests
runner we don't use this method and only need
SimpleFileLoader::selectRunnableTests().

Well of course we can filter runnable tests with
SimpleTest::isIgnored($class) check after calling
selectRunnableTests(), but why really return abstract classes if they
are not actually runnable? Hence the patch ;)

I really hope it's harmless and should not break anything.

-- 
Best regards, Pavel