Bug#561185: xkb-data: support custom layouts

[Ernest Adrogué <nfdisco@gmail.com>]

Package: xkb-data
Version: 2.19-1
Followup-For: Bug #561185

Hello!

Here's a simple solution:

1. Patch base, evdec and xfree98 in /usr/share/X11/xkb/rules/ to include
the following lines:

! model    layout  =  symbols
  *        *       =  +overrides

2. Create a symbolic link to /etc/X11/xkb/symbols/overrides at
/usr/share/X11/xkb/symbols/overrides.

Now the system administrator can remap keys in
/etc/X11/xkb/symbols/overrides without fear that the file will be
overwritten.  For example

cat <<EOF > /etc/X11/xkb/symbols/overrides
partial
xkb_symbols "basic"
{
  override key <AD01>  { [          q,            Q,  parenleft ] };
  override key <AD02>  { [          w,            W, parenright ] };
};
EOF

This method has a big advantage which is that changes take effect both
in X and in the Linux console, therefore users don't end up with
inconsistent key maps in these environments.

Cheers.

-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.11.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=ca_ES.utf8, LC_CTYPE=ca_ES.utf8 (charmap=UTF-8), LANGUAGE=ca_ES.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

-- no debconf information