patch 9.1.1946: Cannot open the help in the current window

Problem:  Cannot open the help in the current window
Solution: Promote the example from tips.txt to a proper package and
          include the helpcurwin package, add tests for it
          (Peter Kenny)

closes: #18840

Signed-off-by: Peter Kenny <github.com@k1w1.cyou>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/Make_all.mak

@@ -244,6 +244,7 @@ NEW_TESTS = \
 	test_perl \
 	test_plugin_comment \
 	test_plugin_glvs \
+	test_plugin_helpcurwin \
 	test_plugin_helptoc \
 	test_plugin_man \
 	test_plugin_matchparen \
@@ -518,6 +519,7 @@ NEW_TESTS_RES = \
 	test_perl.res \
 	test_plugin_comment.res \
 	test_plugin_glvs.res \
+	test_plugin_helpcurwin.res \
 	test_plugin_helptoc.res \
 	test_plugin_man.res \
 	test_plugin_matchparen.res \

src/testdir/test_plugin_helpcurwin.vim

@@ -0,0 +1,13 @@
+" Test for the HelpCurwin package
+
+func Test_helpcurwin_1()
+  packadd helpcurwin
+  call assert_equal(2, exists(':HelpCurwin'))
+  new Xfoobar.txt
+  only
+  HelpCurwin tips.txt
+  call assert_match('.*tips.txt', bufname('%'))
+  call assert_equal(1, winnr('$'))
+  call assert_true(bufexists('Xfoobar.txt'))
+  %bw
+endfunc

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1946,
 /**/
     1945,
 /**/