Personal bash completion and bash ls alias

Let the personal bash completion override the system defaults, that
is source  ~/.bash_completion after the system defaults (bnc#799241).
Make ls an alias to a shell function _ls() which make it possible
to set IFS to e.g. '$\n' and be able to use the command ls (bnc#811030).

Signed-off-by: Werner Fink <werner@suse.de>