At present, 'set args' sets global program arguments -- for every inferior. So,
if you wish to debug multiple programs, and they have different arguments, things
are unpleasant -- arguments should be changed before running each program. The
same problem exists with tty setting. The latter is probably most important for
frontends.

This patch makes 'set args' and 'set inferior-tty' be per-inferior. No regressions
on i686 linux. OK?

- Volodya