- add completion for long options in the same way
  it was defined for the short ones;
- suggest long options when current word starts with '-'.

Suggesting short options (like `-r`) is usually not so useful:
if user does not remember the exact letter, she probably
does not know what the suggested short option does. So,
we suggest long options only.

Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>