patch 9.0.0591: message window popup shows on only one tab page

Problem:    Message window popup shows on only one tab page. (Naruhiko
            Nishino)
Solution:   Show the message window popup on all tab pages. (closes #11231)

src/popupwin.c

@@ -2053,6 +2053,8 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
 	    }
 	}
     }
+    else if (popup_is_notification(type))
+	tabnr = -1;  // show on all tabs
 
     // Create the window and buffer.
     wp = win_alloc_popup_win();

src/testdir/dumps/Test_echowindow_8.dump

@@ -0,0 +1,8 @@
+| +8#0000001#e0e0e08|+| |[|N|o| |N|a|m|e|]| | +2#0000000#ffffff0|[|N|o| |N|a|m|e|]| | +1&&@49|X+8#0000001#e0e0e08
+> +0#0000000#ffffff0@74
+|~+0#4040ff13&| @73
+|═+0#e000002&@74
+|l|a|t|e|r| |m|e|s@1|a|g|e| @61
+|m|o|r|e| @70
+|:+0#0000000&|e|c|h|o|w|i|n| |'|m|o|r|e|'| @59
+@57|0|,|0|-|1| @8|A|l@1| 

src/testdir/test_messages.vim

@@ -475,6 +475,10 @@ func Test_echowindow()
   call term_sendkeys(buf, "\<CR>")
   call VerifyScreenDump(buf, 'Test_echowindow_7', {})
 
+  call term_sendkeys(buf, ":tabnew\<CR>")
+  call term_sendkeys(buf, ":echowin 'more'\<CR>")
+  call VerifyScreenDump(buf, 'Test_echowindow_8', {})
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XtestEchowindow')

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    591,
 /**/
     590,
 /**/