patch 8.0.1224: still interference between test functions

Problem:    Still interference between test functions.
Solution:   Clear autocommands. Wipe all buffers.  Fix tests that depend on a
            specific start context.
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 90a5105..31b6b9f 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -151,7 +151,7 @@
 func XageTests(cchar)
   call s:setup_commands(a:cchar)
 
-  let list = [{'bufnr': 1, 'lnum': 1}]
+  let list = [{'bufnr': bufnr('%'), 'lnum': 1}]
   call g:Xsetlist(list)
 
   " Jumping to a non existent list should return error