Facet restrictions not allowed on xs:decimal types with bad errror

If you have something like this:

<xs:element name="foo">
  <xs:simpleType>
    <xs:restriction base="xs:decimal">
      <xs:minInclusive value="0" />
      <xs:maxInclusive value="10" />
    </xs:restriction>
  </xs:simpleType>
</xs:element>

You get the following unhelpful error message:

[error] Schema Definition Error: checkValueSpaceFacetRange - Unrecognized primitive type: Decimal

Which prevents you from being able to use facet restrictions on xs:decimal types.

It looks like we are just missing a case for Decimal in the checkValueSpaceFacetRange function.

While we're at it, the SDE should also be changed to an Assert, since the catch-all case should never happen except when we have a bug in the logic (like we have now).