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)
diff --git a/src/testdir/test_usercommands.vim b/src/testdir/test_usercommands.vim
index 961aeb2..f8cc1f5 100644
--- a/src/testdir/test_usercommands.vim
+++ b/src/testdir/test_usercommands.vim
@@ -81,6 +81,19 @@
   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
diff --git a/src/usercmd.c b/src/usercmd.c
index 6b3eadc..0160ac1 100644
--- a/src/usercmd.c
+++ b/src/usercmd.c
@@ -1436,7 +1436,24 @@
 
     // :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);
diff --git a/src/version.c b/src/version.c
index f3a7e29..c39a835 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    786,
+/**/
     785,
 /**/
     784,