Splitting commands/cd/cd.sh

As the situation is right now, importing one of the commands the
script replaces, requires a doc/UPDATING step.

By moving the script to a shared folder, and symlinking it once per
command, this allows for separatly installed files on the system,
instead of one file being symlinked multiple times.

Change-Id: I0dae96982bca5168b852ed70fff61442441b929f

commands/shared/README

@@ -0,0 +1,22 @@
+builtin.sh is installed as a set of tools to stand in for specific
+filesystem call to builtin commands.
+
+for example if /bin/test is used, then builtin.sh will be loaded
+and simply call the builtin function of the same name.
+
+At this moment it is installed as the following commands:
+/bin/[
+/bin/command
+/bin/echo
+/bin/expr
+/bin/false
+/bin/getopts
+/bin/read
+/bin/test
+/bin/true
+/bin/umask
+/bin/wait
+
+If one of the following is replaced by the NetBSD equivalent, please
+update the list, and remove this completly when it is not anymore
+required.

commands/shared/builtin.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+#
+# cd 1.3 - equivalents for normally builtin commands.	Author: Kees J. Bot
+
+case $0 in
+*/*)	command="`expr "$0" : '.*/\(.*\)'`"
+	;;
+*)	command="$0"
+esac
+
+"$command" "$@"