#392 Support for XML Schema 1.1

[Alexander Kogtenkov]

Right now the XML plugin works only with XML schema 1.0. In particular, it is possible to edit a user-defined XSD file using XML Schema 1.0 (XMLschema.xsd for version 1.0 from https://www.w3.org/2001/XMLSchema.html).

An attempt to use XML Schema 1.1 (XMLschema.xsd for version 1.1 from the same location) triggers multiple errors.

Most errors are in the form:

...:s4s-att-not-allowed: Attribute '...' cannot appear in element '...'.

And there are a couple of other errors.

In total, the plugin reports 101 errors when trying to use http://www.w3.org/2009/XMLSchema/XMLSchema.xsd (XML schema 1.1) instead of http://www.w3.org/2001/XMLSchema.xsd (XML schema 1.0)

To reproduce:

1. Unpack the archive.
2. Open test.xsd in jEdit.
3. Observe multiple errors due to use of XML Schema 1.1.
4. Rename schemas0.xml to schemas.xml.
5. Observe no errors with XML Schema 1.0.