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_float_func.vim b/src/testdir/test_float_func.vim
index 29bfc9e..6340b53 100644
--- a/src/testdir/test_float_func.vim
+++ b/src/testdir/test_float_func.vim
@@ -1,7 +1,7 @@
 " test float functions
 
 if !has('float')
-  finish
+  throw 'Skipped, float feature missing'
 end
 
 func Test_abs()