Please describe the problem:
Optional attributes declared to have default values in W3C XMLSchemas are not
added to the xmlDoc stucture when they arent specified in an instance document
of that schema. Strangely, the program knows about the defualt value( stored in
the variable iattr->decl at some point in the xmlSchemaVAttributesComplex()
function ), just an error in the logic makes sure the code never gets run that
creates the new attribute node to sit in for the missing attribute.

Steps to reproduce:
1. Create a schema that has elements with optional attributes with a default
specified
2. call xmlSchemaSetValidOptions( schema_validation_context,
XML_SCHEMA_VAL_VC_I_CREATE );
3. validate an instance document that leaves out the optional attributes
4. xmlGetProp( node_with_optional_attributes, defaulted_attribute_name ) returns
null


Actual results:
xmlGetProp( node_with_optional_attributes, defaulted_attribute_name ) returns null

Expected results:
xmlGetProp( node_with_optional_attributes, defaulted_attribute_name ) returns
the string representation of the default value


Does this happen every time?
yes

Other information:
============Schema=================
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified"
           attributeFormDefault="unqualified"
           xml:lang="en">

       <xs:element name="DefaultAttributeTest">
        <xs:complexType>
            <xs:attribute name="optional1" type="xs:integer"
                          use="optional" default="1"/>
            <xs:attribute name="optional2" type="xs:integer"
                          use="optional" default="2"/>
            <xs:attribute name="optional3" type="xs:integer"
                          use="optional" default="3"/>
            <xs:attribute name="override1000with2" type="xs:integer"
                          use="optional" default="1000"/>
            <xs:attribute name="optional4" type="xs:integer"
                          use="optional" default="4"/>
            <xs:attribute name="optional5" type="xs:integer"
                          use="optional" default="5"/>
            <xs:attribute name="optional6" type="xs:integer"
                          use="optional" default="6"/>
            <xs:attribute name="optional7" type="xs:integer"
                          use="optional" default="7"/>
        </xs:complexType>
    </xs:element>
</xs:schema>
===================================

============Instance===============
<?xml version="1.0" encoding="UTF-8"?>
<DefaultAttributeTest
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="default-attributes.xsd"
    override1000with2="2"/>

===================================
I tracked down the problem to here where defualt values get filled in.

http://cvs.gnome.org/viewcvs/*checkout*/libxml2/xmlschemas.c?rev=1.201

iattr->node on an optional attribute that isnt present is always null. Whereever
this "iattr" struct is getting built they forgot to build a(n attribute)node for it.
iattr->decl->defValue has the defualt value needed, but I'm too lost in the
logic of the code to provide a fix of my own.

static int
xmlSchemaVAttributesComplex(xmlSchemaValidCtxtPtr vctxt)
line 25137 of schemas.c 

	    /*
	    * PSVI: Add the default attribute to the current element.
	    * VAL TODO: Should we use the *normalized* value? This currently
	    *   uses the *initial* value.
	    */
	    if ((vctxt->options & XML_SCHEMA_VAL_VC_I_CREATE) &&
		(iattr->node != NULL) && (iattr->node->doc != NULL)) {
		xmlChar *normValue;
		const xmlChar *value;

		value = iattr->value;
		/*
		* Normalize the value.
		*/
		normValue = xmlSchemaNormalizeValue(iattr->typeDef,
		    iattr->value);
		if (normValue != NULL)
		    value = BAD_CAST normValue;

		if (iattr->nsName == NULL) {
		    if (xmlNewProp(iattr->node->parent,
			iattr->localName, value) == NULL) {
			VERROR_INT("xmlSchemaVAttributesComplex",
			    "callling xmlNewProp()");
			if (normValue != NULL)
			    xmlFree(normValue);