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_crypt.vim b/src/testdir/test_crypt.vim
index bf1a511..db10099 100644
--- a/src/testdir/test_crypt.vim
+++ b/src/testdir/test_crypt.vim
@@ -1,7 +1,7 @@
 " Tests for encryption.
 
 if !has('cryptv')
-  finish
+  throw 'Skipped, encryption feature missing'
 endif
 
 func Common_head_only(text)