patch 8.1.1524: tests are silently skipped

Problem:    Tests are silently skipped.
Solution:   Throw an exception for skipped tests in more places.
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index ef0a512..2fa28c9 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -1,7 +1,7 @@
 " Test for the quickfix feature.
 
 if !has('quickfix')
-  finish
+  throw 'Skipped, quickfix feature missing'
 endif
 
 set encoding=utf-8