Translate ISO_Left_Tab to Meta_Tab

Short description: ISO_Left_Tab shouldn't be translated to Tab (just like regular Tab) otherwise there's no way to differentiate between Tab and Shift-Tab on text mode. This commit changes ckbcomp to translate ISO_Left_Tab to Meta_Tab.

Long description: Currently, in most Linux distribution, most keyboard layouts in text mode assign the Tab and Shift-Tab key presses the same code. This can be checked by pressing ctrl-alt-f1, logging in and running: "showkey -a"

Pressing Tab and Shift-Tab generate the same code (0x09), so for example, when Yast runs with ncurses, Tab moves the focus to the next focusable item, but Shift-Tab can't be used as it behaves just like Tab and there's no way applications can differentiate both.

Changing the keyboard layout with "loadkeys es", "loadkeys de" or "loadkeys fr" doesn't help.

I investigated this and found that ckbcomp was translating the ISO_Left_Tab symbol to Tab just like it does with Tab, which doesn't make sense since Shift-Tab should produce a "Left Tab" (in many keyboards it's even printed in the Tab key over the regular Right-Tab drawing).

Looking at how the keyboard layouts were defined before xkb layouts were parsed, I noticed legacy layouts were defined like:

keycode 15 = Tab
    shift  keycode 15 = Meta_Tab

So ISO_Left_Tab is now translated to Meta_Tab to fix this and let it generate the same code it did in the past.

Now "showkey -a" shows the (0x09) code for Tab and (0x1b 0x09) for Shift-Tab which can be recognized by text applications as different and automatically fixes Yast.

In SUSE/openSUSE distributions, after applying this change and rebuilding the kbd package with the generated console-setup (which regenerates the kbd keymaps with the fixed ckbcomp script) fixes this. I guess other distributions would also need to rebuild kbd after applying this patch.