xsd:decimal: fix representation
xsd:decimal: fix representation

repr(v) for an xsd.decimal instance was coming out as "Decimal('0.0')",
which is wrong for generated bindings which don't import that class by
that name.

CantemoInternal/pyxb,CantemoInternal/pyxb,pabigot/pyxb,pabigot/pyxb,CantemoInternal/pyxb