Don't clobber `in` and `name` fields in body/form parameters

Fixes #2.  I'll try to follow this up with a corresponding test script.
I'm not sure if this is the right fix. Isn't the bug that I'm changing $p, which is an alias for the elements in the ```$config->{parameters}``` list? I think the fix is to do this instead:

    for (@{$config->{parameters} || []}) {
      my $p = $_;
      ...

That way, $p is not an alias, but simply a variable.