Implemented goto_tab_nn using Alt+Fn like in Linux console

This may potentially break existing console applications which use Alt-Fn
for something.  In that case, the fix is to add the following to one's
.Xresources:

urxvt.tabbed.no-tabbedex-keys: yes
urxvt.keysym.Shift-Left: perl:tabbedex:prev_tab
urxvt.keysym.Shift-Right: perl:tabbedex:next_tab
urxvt.keysym.Shift-Down: perl:tabbedex:new_tab
urxvt.keysym.Shift-Up: perl:tabbedex:rename_tab
urxvt.keysym.Control-Left: perl:tabbedex:move_tab_left
urxvt.keysym.Control-Right: perl:tabbedex:move_tab_right

In case no-tabbedex-keys is already used, to enable goto_tab_nn bindings
the following needs to be added instead:

urxvt.keysym.Meta-F1: perl:tabbedex:goto_tab_1
urxvt.keysym.Meta-F2: perl:tabbedex:goto_tab_2
urxvt.keysym.Meta-F3: perl:tabbedex:goto_tab_3
urxvt.keysym.Meta-F4: perl:tabbedex:goto_tab_4
urxvt.keysym.Meta-F5: perl:tabbedex:goto_tab_5
urxvt.keysym.Meta-F6: perl:tabbedex:goto_tab_6
urxvt.keysym.Meta-F7: perl:tabbedex:goto_tab_7
urxvt.keysym.Meta-F8: perl:tabbedex:goto_tab_8
urxvt.keysym.Meta-F9: perl:tabbedex:goto_tab_9
urxvt.keysym.Meta-F10: perl:tabbedex:goto_tab_10
urxvt.keysym.Meta-F11: perl:tabbedex:goto_tab_11
urxvt.keysym.Meta-F12: perl:tabbedex:goto_tab_12

[mina86@mina86.com: Changed Meta-F<n> bindings to a simple loop
 and added more a detailed commit message.]

tabbedex

@@ -3,7 +3,7 @@
 ## TabbedEx plugin for rxvt-unicode
 ## Based on original tabbed plugin.
 ## Copyright (c) 2006-2012 tabbed authors
-## Copyright (c) 2009-2013 tabbedex authors
+## Copyright (c) 2009-2014 tabbedex authors
 ##
 ## This program is free software: you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -514,6 +514,10 @@ sub register_keysyms {
         $tab->parse_keysym('Shift-Up', 'perl:tabbedex:rename_tab');
         $tab->parse_keysym('Control-Left', 'perl:tabbedex:move_tab_left');
         $tab->parse_keysym('Control-Right', 'perl:tabbedex:move_tab_right');
+        for my $num (1..12) {
+            $tab->parse_keysym('Meta-F' . $num,
+                               'perl:tabbedex:goto_tab_' . $num);
+        }
     }
 }
 
@@ -726,6 +730,9 @@ sub tab_user_command {
   elsif ($cmd eq 'tabbedex:move_tab_right') {
     $self->move_tab($tab, 1);
   }
+  elsif ($cmd =~ /^tabbedex:goto_tab_(\d+)$/) {
+    $self->change_to_tab($tab, $1 - 1);
+  }
   elsif ($cmd eq 'tabbedex:rename_tab') {
     $self->rename_tab($tab);
   }
@@ -755,6 +762,16 @@ sub change_tab {
     ();
 }
 
+sub change_to_tab {
+    my ($self, $tab, $idx) = @_;
+
+    if (!$self->{is_inputting_name} && @{ $self->{tabs} } > 1 && $idx >= 0 && $idx < @{ $self->{tabs} }) {
+        $self->make_current ($self->{tabs}[$idx]);
+    }
+
+    ();
+}
+
 sub move_tab {
   my ($self, $tab, $direction) = @_;