Version matching for a PolicySetIdReference

Hi,

when reading the text of XACML-3.0wd06, section 5.10, I suspected an
error in the specification. According to the text, the following
reference would not accept a policy set having version "2.0".

<PolicySetIdReference earliestVersion="1.0" latestVersion="3.0">

To resolve this issue, there needs to be a total ordering among Version,
which takes care of such special values like "0.000", "0.01", that is,
it cannot just use the lexicographic comparison among strings.

Roland