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_textobjects.vim b/src/testdir/test_textobjects.vim
index 0baabc0..5366a35 100644
--- a/src/testdir/test_textobjects.vim
+++ b/src/testdir/test_textobjects.vim
@@ -1,7 +1,7 @@
 " Test for textobjects
 
 if !has('textobjects')
-  finish
+  throw 'Skipped, textobjects feature missing'
 endif
 
 func CpoM(line, useM, expected)