patch 9.0.0786: user command does not get number from :tab modifier

Problem:    User command does not get number from :tab modifier.
Solution:   Include the number. (closes #11393, closes #6801)

src/testdir/test_usercommands.vim

@@ -81,6 +81,19 @@ function Test_cmdmods()
   call assert_equal('silent!', g:mods)
   tab MyCmd
   call assert_equal('tab', g:mods)
+  0tab MyCmd
+  call assert_equal('0tab', g:mods)
+  tab split
+  tab MyCmd
+  call assert_equal('tab', g:mods)
+  1tab MyCmd
+  call assert_equal('1tab', g:mods)
+  tabprev
+  tab MyCmd
+  call assert_equal('tab', g:mods)
+  2tab MyCmd
+  call assert_equal('2tab', g:mods)
+  2tabclose
   topleft MyCmd
   call assert_equal('topleft', g:mods)
   to MyCmd

src/usercmd.c

@@ -1436,7 +1436,24 @@ add_win_cmd_modifers(char_u *buf, cmdmod_T *cmod, int *multi_mods)
 
     // :tab
     if (cmod->cmod_tab > 0)
-	result += add_cmd_modifier(buf, "tab", multi_mods);
+    {
+	int tabnr = cmod->cmod_tab - 1;
+
+	if (tabnr == tabpage_index(curtab))
+	{
+	    // For compatibility, don't add a tabpage number if it is the same
+	    // as the default number for :tab.
+	    result += add_cmd_modifier(buf, "tab", multi_mods);
+	}
+	else
+	{
+	    char tab_buf[NUMBUFLEN + 3];
+
+	    sprintf(tab_buf, "%dtab", tabnr);
+	    result += add_cmd_modifier(buf, tab_buf, multi_mods);
+	}
+    }
+
     // :topleft
     if (cmod->cmod_split & WSP_TOP)
 	result += add_cmd_modifier(buf, "topleft", multi_mods);

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    786,
 /**/
     785,
 /**/