[xml] XML Schema engine changes

[Kasimier Buchcik <kbuchcik 4commerce de>]

Hi,

the following changes have been applied to the XML Schema engine of libxml2:

1. Modified parsing of <list>
2. Modified parsing of <union>
3. Modified parsing of <restriction>
4. Modified parsing of <sequence>
5. Modified parsing of <choice>
6. Modified parsing of <include>
7. Added handling of schema defaults (elementFormDefault, etc.) for
   included schemas.
8. Fixed a bug which reported attributes as invalid on elements
   declarations with the built-in type 'anyType'.
   Added "lax" validation of the content of elements of type 'anyType'.
9. Changed parsing of <import>
10. Fixed: element declarations with the same name were treated
   as dublicate if located in the subtree of <choice> -> <sequence>.
   (This was bug 150623, submitted by Roland Lezuo)
11. Fixed cleanup of error codes in xmlSchemaValidateDoc as proposed by
   Igor Kapitanker. (This was bug 150647, submitted by Igor Kapitanker)
12. Added and changed regression tests.
13. Begin (not yet plugged in) of the implementation of constraints on
   derivation of complex types.


Greetings,

Kasimier