This patch covers one big part of variable handling.

This patch covers one big part of variable handling.
$ a=b foo
should be handled correctly.
$ a=b
is parsed OK, but the actual variable setting is not
yet written.  Except for some weird exceptions related
to quoting rules, this code passes (matches ash behavior)
all the tests I threw at it.

If someone now writes set_local_var(), and updates lookup_param()
to match, we can claim success!

       - Larry