patch 8.0.1844: superfluous quickfix code, missing examples

Problem:    Superfluous quickfix code, missing examples.
Solution:   Remove unneeded code.  Add a few examples.  Add a bit more
            testing. (Yegappan Lakshmanan, closes #2916)
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 985b281..c3850ce 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -1185,6 +1185,13 @@
   call assert_equal(1, len(l), string(l))
   call assert_equal('|| msg2', l[0].text)
 
+  " When matching error lines, case should be ignored. Test for this.
+  set noignorecase
+  let l=getqflist({'lines' : ['Xtest:FOO10:Line 20'], 'efm':'%f:foo%l:%m'})
+  call assert_equal(10, l.items[0].lnum)
+  call assert_equal('Line 20', l.items[0].text)
+  set ignorecase&
+
   new | only
   let &efm = save_efm
 endfunc