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_cscope.vim b/src/testdir/test_cscope.vim
index 7795ac7..a3fcbd7 100644
--- a/src/testdir/test_cscope.vim
+++ b/src/testdir/test_cscope.vim
@@ -1,7 +1,10 @@
 " Test for cscope commands.
 
-if !has('cscope') || !executable('cscope') || !has('quickfix')
-  finish
+if !has('cscope') || !has('quickfix')
+  throw 'Skipped, cscope or quickfix feature missing'
+endif
+if !executable('cscope')
+  throw 'Skipped, cscope program missing'
 endif
 
 func CscopeSetupOrClean(setup)