patch 9.1.1419: It is difficult to ignore all but some events

Problem:  It is difficult to ignore all but some events.
Solution: Add support for a "-" prefix syntax in '(win)eventignore' that
          subtracts an event from the ignored set if present
          (Luuk van Baal).

closes: #17392

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 8679198..e85dd6a 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -602,6 +602,7 @@
 
   " Other string options that queries the system rather than fixed enum names
   call assert_equal(['all', 'BufAdd'], getcompletion('set eventignore=', 'cmdline')[0:1])
+  call assert_equal(['-BufAdd', '-BufCreate'], getcompletion('set eventignore=all,-', 'cmdline')[0:1])
   call assert_equal(['WinLeave', 'WinResized', 'WinScrolled'], getcompletion('set eiw=', 'cmdline')[-3:-1])
   call assert_equal('latin1', getcompletion('set fileencodings=', 'cmdline')[1])
   call assert_equal('top', getcompletion('set printoptions=', 'cmdline')[0])