ACTION-126: schema part 2 reference needs update (sorry...)

In 4.3.3.1 [1], we refer to XMLSCHEMA Datatypes, 2nd Edition.
However, the references section includes a link to the 2nd edition
of XML Schema Part 1, and a link to the first edition of XML Schema
Part 2.

This looks like an editorial oversight to me.   I therefore propose
the following changes:

- separate bibliography entries for schema part 1 and schema part 2
- change reference in 4.3.3.1 to comply with usual referencing
  conventions
- update link in references to 2nd edition of schema part 2

1. http://www.w3.org/2007/xmlsec/Drafts/xmldsig-core/#sec-URI

Regards,
-- 
Thomas Roessler, W3C  <tlr@w3.org>