bug#10317: patch to su: -l and -p should not be used together

[Rocky Bernstein]

Hi -

I noticed that -m (-p, --preserve-environment) and -l (- --login) can't be
used together.

Attached is a patch to give a warning if they are and to indicate which
option is used. In the code, I opted for the earlier option ignoring the
later option. In the code --login has precedence over
--preserve-environment.

su-l-vs-p.diff
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