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_windows_home.vim b/src/testdir/test_windows_home.vim
index 2e311b9..da95ed2 100644
--- a/src/testdir/test_windows_home.vim
+++ b/src/testdir/test_windows_home.vim
@@ -1,7 +1,7 @@
 " Test for $HOME on Windows.
 
 if !has('win32')
-  finish
+  throw 'Skipped, not on MS-Windows'
 endif
 
 let s:env = {}