helper/command: register full-name commands in jim

helper/command: register full-name commands in jim

While still keeping the tree of struct command, stop registering
commands in jim by the root "word" only.

Register the full-name of the command and pass as private data the
struct command of the command itself.

Still use the tree of struct command to un-register the commands.

Some "native" commands (.jim_handler) share the same handler, then
the handler checks the command name to run the right code.
Now argv[0] returns the full-name of the command, so check the
name by looking in the struct command passed as private data.

Change-Id: I5623c61cceee8a75f5d5a551ef3fbf5a303af6be
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5671
Tested-by: jenkins
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>