bug#18105: term, ansi-term: allow to pass arguments to command

[Carlos Pita]

It's a somewhat surprising limitation that M-x term doesn't take
further (optional) command line parameters to pass to `PROGRAM`. The
underlying workhorse functions do take a `switches` parameters, so
this is more of a frontend matter than a real limitation in term.el.
Please change the interactive functions `term` and `ansi-term` to take
further arguments to be passed to exec. This would be a simple change,
backwards compatible and more Unix-friendly (I can't think of a
command apart from its arguments).