[RFA] add test for memattr, use get_number_or_range for memattr commands

[Joel Brobecker]

> Hmmm, how about if I initialize mem1start etc. to -1?
> Then the rest of the tests will fail but not crash.
> Is that better?

Yep, that would work for me. You could also do something like this:

    if {![info exists mem1start] || ![info exists mem2start] ...} {
        fail "..."
        # No point in continuing the rest of the testcase if we couldn't
        # get the addresses we need bla bla bla.
        return
    }

-- 
Joel