Get or set the six fields of a Gtk2::Adjustment.

The setter functions store $newval and return the old value. Note that they don't emit any signals; it's up to you to emit "notify" (because the fields are also properties) and "changed" or "value-changed", when you're ready.

These functions differ from the plain ->lower etc setters in that they emit notify and changed signals if $newval is different from the current value.

The corresponding get_lower etc are not wrapped because they're the same as the lower etc field accessors above.